C5 security issue???
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
This one is a generic bulletin from the Shop Manual and is not Vette specific but it refers to the causes of a low voltage light.
The other thing you could check is whether you have a draw which is pulling your battery down. Bill Curlee posted a How To which shows how to identify a current drain. If you go through that guide and make sure there isn't something shorting out. I'll try to find it and post a link.
Info - Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output #02-06-03-008A - (07/28/2004)
Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output
1990-2005 Passenger Cars and Light Duty Trucks
Any vehicle may have a low voltage display (if equipped with gauges), lights that dim at stop lights, slow cranking, no start, low generator output at idle or dim lights at idle when electrical loads are heavy at idle or under slow driving or infrequent usage conditions. These characteristics may be more noticeable with customer added electrical accessories, or with a discharged battery. These are normal operating characteristics of a vehicle electrical system and no repairs should be attempted unless a proven fault has been diagnosed.
During normal driving conditions, when engine speed is above 1000 RPM, the generator is designed to do two things:
* Supply the current necessary to operate the vehicle's originally equipped electrical devices (loads).
* Recharge/ maintain the battery's state of charge.
The following factors may affect generator and battery performance:
* Non-usage of the vehicle for extended periods of time. The vehicle's computers, clocks and the like will cause the battery state of charge to drop (For example; 30 days in a parking lot and the vehicle may not start because of a dead battery or a vehicle which is driven only a short distance once a week may end up with a discharged battery to the point where the vehicle may not start). This would be considered abnormal usage of the vehicle and the normally expected result for the vehicle battery, generator and electrical systems.
* At idle, vehicle electrical loads may exceed the low speed current (amperage) output of the generator and when this happens the shortfall comes from the battery. This will result in a drop in the electrical system voltage as the battery delivers the additional electrical current to meet the demand. This is equivalent to the brown outs experienced by homes and businesses when the electrical demand is more than the supply. See Figure 1.
* Extended periods of engine idling, with high electrical loads, may result in a discharged battery. Attempting to recharge a battery by letting the engine run at idle may not be beneficial unless all electrical loads are turned "OFF".
* Increased internal generator temperatures from extended idling can also contribute to lower electrical system voltage. As the generator's internal temperature rises, the generator's output capability is reduced due to increased electrical resistance.
The following are some typical examples of electrical loads:
System/ Amperage Load
Rear Window defogger/ 25
Electric AIR Pump/25
Heated Seats/5 Amps per seat
Headlamps (high)/20
Blower Motor (High)/20
Headlamps (low)/15
Brake Lights/6
Windshield Wipers/6
Ignition/6
Depending on the vehicle application, generator current (amperage) output at engine idle speeds of 600-700 RPM can be as low as 35 percent of the full rated output. With enough electrical loads "ON", it is easy to exceed the generator current (amperage) output when the engine is at an idle of 600-700 RPM. This is a normal condition. The battery supplements for short periods of time. Items that affect the vehicle's electrical system current and voltage at idle are the number of electrical loads being used, including add-on accessories, and extended idle times. When the vehicle speed is above approximately 24 km/h (15 mph), the engine/generator RPM is high enough and the generator current (amperage ) output is sufficient to supply the current (amperage) requirements of the vehicle as originally equipped and recharge the battery.
Dimming lights at idle may be considered normal for two reasons:
1. As the engine/generator speed changes, so will the current (amperage) output of the generator. As a vehicle slows, engine/generator RPM slows, and the current (amperage) output of the generator may not be sufficient to supply the loads, the vehicle system voltage will drop and the lights will dim. Dimming of the lights is an indication that current is being pulled from the battery. If the battery is in a low state-of-charge (discharged condition), the driver will notice a more pronounced dimming than a vehicle with a fully charged battery.
2. When high current loads (blower, rear defogger, headlamps, cooling fan, heated seats, power seats, electric "AIR" pump, or power windows) are operating or cycled "ON", the generator's voltage regulator can delay the rise in output. This effect, usually at lower engine speeds, can take up to ten seconds to ramp up the generator output. This is done to avoid loading the engine severely. To increase current (amperage) output, additional torque is consumed by the generator. The engine computer (PCM) will ramp up engine/generator speed in small steps so engine speed variations are not noticeable to the driver.
For diagnosis of the battery and or the generator, refer to the appropriate Service Information or Corporate Bulletin Number 02-06-03-006A.
The other thing you could check is whether you have a draw which is pulling your battery down. Bill Curlee posted a How To which shows how to identify a current drain. If you go through that guide and make sure there isn't something shorting out. I'll try to find it and post a link.
Info - Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output #02-06-03-008A - (07/28/2004)
Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output
1990-2005 Passenger Cars and Light Duty Trucks
Any vehicle may have a low voltage display (if equipped with gauges), lights that dim at stop lights, slow cranking, no start, low generator output at idle or dim lights at idle when electrical loads are heavy at idle or under slow driving or infrequent usage conditions. These characteristics may be more noticeable with customer added electrical accessories, or with a discharged battery. These are normal operating characteristics of a vehicle electrical system and no repairs should be attempted unless a proven fault has been diagnosed.
During normal driving conditions, when engine speed is above 1000 RPM, the generator is designed to do two things:
* Supply the current necessary to operate the vehicle's originally equipped electrical devices (loads).
* Recharge/ maintain the battery's state of charge.
The following factors may affect generator and battery performance:
* Non-usage of the vehicle for extended periods of time. The vehicle's computers, clocks and the like will cause the battery state of charge to drop (For example; 30 days in a parking lot and the vehicle may not start because of a dead battery or a vehicle which is driven only a short distance once a week may end up with a discharged battery to the point where the vehicle may not start). This would be considered abnormal usage of the vehicle and the normally expected result for the vehicle battery, generator and electrical systems.
* At idle, vehicle electrical loads may exceed the low speed current (amperage) output of the generator and when this happens the shortfall comes from the battery. This will result in a drop in the electrical system voltage as the battery delivers the additional electrical current to meet the demand. This is equivalent to the brown outs experienced by homes and businesses when the electrical demand is more than the supply. See Figure 1.
* Extended periods of engine idling, with high electrical loads, may result in a discharged battery. Attempting to recharge a battery by letting the engine run at idle may not be beneficial unless all electrical loads are turned "OFF".
* Increased internal generator temperatures from extended idling can also contribute to lower electrical system voltage. As the generator's internal temperature rises, the generator's output capability is reduced due to increased electrical resistance.
The following are some typical examples of electrical loads:
System/ Amperage Load
Rear Window defogger/ 25
Electric AIR Pump/25
Heated Seats/5 Amps per seat
Headlamps (high)/20
Blower Motor (High)/20
Headlamps (low)/15
Brake Lights/6
Windshield Wipers/6
Ignition/6
Depending on the vehicle application, generator current (amperage) output at engine idle speeds of 600-700 RPM can be as low as 35 percent of the full rated output. With enough electrical loads "ON", it is easy to exceed the generator current (amperage) output when the engine is at an idle of 600-700 RPM. This is a normal condition. The battery supplements for short periods of time. Items that affect the vehicle's electrical system current and voltage at idle are the number of electrical loads being used, including add-on accessories, and extended idle times. When the vehicle speed is above approximately 24 km/h (15 mph), the engine/generator RPM is high enough and the generator current (amperage ) output is sufficient to supply the current (amperage) requirements of the vehicle as originally equipped and recharge the battery.
Dimming lights at idle may be considered normal for two reasons:
1. As the engine/generator speed changes, so will the current (amperage) output of the generator. As a vehicle slows, engine/generator RPM slows, and the current (amperage) output of the generator may not be sufficient to supply the loads, the vehicle system voltage will drop and the lights will dim. Dimming of the lights is an indication that current is being pulled from the battery. If the battery is in a low state-of-charge (discharged condition), the driver will notice a more pronounced dimming than a vehicle with a fully charged battery.
2. When high current loads (blower, rear defogger, headlamps, cooling fan, heated seats, power seats, electric "AIR" pump, or power windows) are operating or cycled "ON", the generator's voltage regulator can delay the rise in output. This effect, usually at lower engine speeds, can take up to ten seconds to ramp up the generator output. This is done to avoid loading the engine severely. To increase current (amperage) output, additional torque is consumed by the generator. The engine computer (PCM) will ramp up engine/generator speed in small steps so engine speed variations are not noticeable to the driver.
For diagnosis of the battery and or the generator, refer to the appropriate Service Information or Corporate Bulletin Number 02-06-03-006A.
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Here's the check procedure for the electrical system. Unfortunately were still back at the modules not communicating over the data bus. As you can see, the first thing the Tech would test is whether the individual modules are communicating (using a Tech II)
Diagnostic System Check - Engine Electrical
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Lack of communication may be because of a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
The symptom list in Symptoms will determine the correct diagnostic procedure to use.
The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will collect all the available information before you perform tests.
Step
Action
Yes
No
1
Perform the Battery Inspection/Test. Refer to Battery Inspection/Test .
Does the battery pass the test?
Go to Step 2
--
2
1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
Does the scan tool power up?
Go to Step 3
Go to Scan Tool Does Not Power Up in Data Link Communications
3
1. Turn ON the ignition, with the engine OFF.
2. Attempt to communicate with each of the following modules on the class 2 serial data circuit:
* Body Control Module (BCM)
* Left Door Control Module (LDCM)
* Right Door Control Module (RDCM)
* Seat Control Module (SCM)
* Powertrain Control Module (PCM)
Does the scan tool communicate with all modules on the class 2 serial data circuit?
Go to Step 4
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
4
1. Select the Display DTCs function for each module. (If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set.)
2. Record all of the displayed DTCs, the DTC status, and the module which set the DTC.
Does the scan tool display any DTCs?
Go to Step 5
Go to Symptoms - Engine Electrical
5
Does the scan tool display any DTCs which begin with a U?
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
Go to Step 6
6
Does the scan tool display DTC B1000?
Go to Diagnostic Trouble Code (DTC) List in Body Control System
Go to Diagnostic Trouble Code (DTC) List
Diagnostic System Check - Engine Electrical
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Lack of communication may be because of a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
The symptom list in Symptoms will determine the correct diagnostic procedure to use.
The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will collect all the available information before you perform tests.
Step
Action
Yes
No
1
Perform the Battery Inspection/Test. Refer to Battery Inspection/Test .
Does the battery pass the test?
Go to Step 2
--
2
1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
Does the scan tool power up?
Go to Step 3
Go to Scan Tool Does Not Power Up in Data Link Communications
3
1. Turn ON the ignition, with the engine OFF.
2. Attempt to communicate with each of the following modules on the class 2 serial data circuit:
* Body Control Module (BCM)
* Left Door Control Module (LDCM)
* Right Door Control Module (RDCM)
* Seat Control Module (SCM)
* Powertrain Control Module (PCM)
Does the scan tool communicate with all modules on the class 2 serial data circuit?
Go to Step 4
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
4
1. Select the Display DTCs function for each module. (If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set.)
2. Record all of the displayed DTCs, the DTC status, and the module which set the DTC.
Does the scan tool display any DTCs?
Go to Step 5
Go to Symptoms - Engine Electrical
5
Does the scan tool display any DTCs which begin with a U?
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
Go to Step 6
6
Does the scan tool display DTC B1000?
Go to Diagnostic Trouble Code (DTC) List in Body Control System
Go to Diagnostic Trouble Code (DTC) List
Last edited by DeeGee; Jul 20, 2010 at 03:25 AM.
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
And here's the procedure for no communication:
You dont have the U1300, U1301, or U1305 codes but you do have the U1000
Scan Tool Does Not Communicate with Class 2 Device
Circuit Description
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation when operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Multiple diagnostic trouble codes (DTCs) may be set due to this malfunction and during this diagnostic procedure. Complete the diagnostic procedure in order to be sure all the DTCs are diagnosed and cleared from memory.
Diagnostic Aids
* When the class 2 serial data circuit is shorted to ground, U1300 will be set. Refer to DTC U1300, U1301, or U1305 .
* When the class 2 serial data circuit is shorted to B+, U1301 will be set. Refer to DTC U1300, U1301, or U1305 .
* Disconnecting modules and turning the ignition switch to RUN may cause DTCs in the vehicle modules. Check for DTCs in each module upon completion of the required repair.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2.
A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial data circuit:
* Body Control Module (BCM)
* Electronic Brake Control Module (EBCM)
* Electronic Suspension Control (ESC)
* HVAC with CJ2
* Sensing and Diagnostic Module (SDM)
* Instrument Panel Cluster (IPC)
* Driver Door Module (DDM)
* Passenger Door Module (PDM)
* Seat Control Module (SCM) with AAB
* Powertrain Control Module (PCM)
* Radio
* Remote Control Door Lock Receiver (RCDLR)
A DTC indicating loss of communications with a particular module with a history status may be present along with a U1000 or U1255 having a current status. This indicates that the malfunction occurred when the ignition was ON.
Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
A poor connection at the star connectors will cause multiple communication DTCs to set.
An open in the class 2 serial data circuit between the DLC and one of the star connectors will prevent the scan tool from communicating with some modules. This condition will cause multiple communication DTCs to set.
This test isolates the BCM by using the J 42236 Serial Data Link Tester and a scan tool. The BCM monitors the ignition switch position and sends the appropriate power mode message to other modules. The BCM must be communicating before attempting to diagnose communication DTCs.
This test isolates each module on star connector #1 by communicating with each module separately using the J 42236 Serial Data Link Tester and a scan tool.
This test isolates each module on star connector #2 by communicating with each module separately using the J 42236 Serial Data Link Tester and a scan tool.
If there are no current DTC's that begin with a "U", the communication malfunction has been repaired.
The communication malfunction may have prevented diagnosis of the customer complaint.
Step
Action
Yes
No
1
Does the scan tool power up?
Go to Step 2
Go to Scan Tool Does Not Power Up
2
1. Turn ON the ignition with the engine OFF.
2. Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the Class 2 Message Monitor feature.
Does the scan tool communicate with any module on the class 2 serial data circuit?
Go to Step 3
Go to Step 9
3
1. Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.
Did you record any DTCs in the range of U1000 to U1305?
Go to Step 4
Go to Diagnostic Aids
4
Are the DTCs U1300, U1301 or U1305 retrieved from any module?
Go to Step 5
Go to Step 6
5
Important
Turn on the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.
Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following in Wiring Systems:
* Testing for Intermittent and Poor Connections
* Circuit Testing
* Connector Repairs
* Wiring Repairs
Did you find and correct the condition?
Go to Step 15
Go to Step 6
6
Is U1000 or U1255 the only DTC displayed in the previously specified range?
Go to DTC U1000 and U1255
Go to DTC U1001-U1254
7
1. Turn OFF the ignition.
2. Disconnect the scan tool from the data link connector (DLC).
3. Inspect for poor connections at the DLC terminals 2 and 5. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 8
8
Test the ground circuit of the DLC terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 9
9
1. Disconnect the bus bars from star connector #1 and star connector #2.
2. Inspect for poor connections at the star connectors. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 10
10
Test the class 2 serial data circuit for an open or a short between the DLC connector and the star connectors. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 11
11
1. Turn OFF the ignition.
2. Install a scan tool.
3. Disconnect the bus bars from star connector #1 and star connector #2.
4. Connect J 42236 Serial Data Link Tester to both star connectors.
Important
Ensure the vehicle star connector #1 and star connector #2 correctly correspond with the Serial Data Link Tester connector #1 and connector #2. Refer to Data Link Connector (DLC) Schematics .
5. Place the switch located on the Serial Data Link Tester in the STAR CONNECTOR #1 position.
6. Rotate the rotary switch to the (M) position.
7. Turn ON the ignition with the engine OFF.
8. Attempt to communicate with the BCM.
Does the scan tool communicate with the BCM?
Go to Step 12
Go to Step 14
12
1. Place the switch located on the Serial Data Link Tester to the STAR CONNECTOR #1 position.
2. Use a scan tool and attempt to communicate with each of the following systems by rotating the rotary switch on the Serial Data Link Tester in the following positions. The Tech 2 Diagnostic Circuit Check/Class 2 Message Monitor may be used to display communication status with all systems:
* (L) = HVAC with CJ2
* (J) = RCDLR
* (H) = ESC
* (G) = IPC
* (F) = SDM
* (E) = EBCM
* (D) = RADIO
* (B) = PCM
Does the scan tool communicate with all of the systems?
Go to Step 13
Go to Step 14
13
1. Place the switch located on the Serial Data Link Tester to the STAR CONNECTOR #2 position.
2. Use a scan tool and attempt to communicate with each of the following systems by rotating the rotary switch on the Serial Data Link Tester in the following positions. The Tech 2 Diagnostic Circuit Check/Class 2 Message Monitor may be used to display communication status with all systems:
* (C) = DDM
* (D) = PDM
* (K) = SCM (with AAB
Does the scan tool communicate with all of the systems?
Go to Step 17
Go to Step 14
14
1. Turn OFF the ignition.
2. Disconnect the module that is not communicating.
3. Test the class 2 serial data circuit between the star connector and the module that is not communicating for a short to ground or a short to voltage. Turn ON the ignition with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 17
Go to Step 15
15
Inspect for poor connections at the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 17
Go to Step 16
16
Important
Perform the set up procedure for module if required.
Replace the module which is not communicating. Refer to Control Module References in Body Control System.
Did you complete the replacement?
Go to Step 17
--
17
1. Reconnect all of the disconnected modules.
2. Reconnect any other disconnected connectors.
3. Install a scan tool.
4. Turn ON the ignition with the engine OFF.
5. Wait for 10 seconds.
6. The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn OFF or disconnect the scan tool prior to performing this test. Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
7. Record all of the displayed DTCs and the DTC status.
Did you record any DTCs which begin with a "U" and with a current status?
Go to Step 19
Go to Step 18
18
Did you record any DTCs which do not begin with a "U"?
Go to Step 19
Go to Step 21
19
Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to Control Module References in Body Control System for the applicable Diagnostic System Check.
Did you complete the action?
Go to Step 20
--
20
Did you diagnose all of the DTCs?
Go to Step 21
Go to Step 19
21
Use the scan tool in order to clear the DTCs.
Did you complete the action?
System OK
--
You dont have the U1300, U1301, or U1305 codes but you do have the U1000
Scan Tool Does Not Communicate with Class 2 Device
Circuit Description
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation when operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Multiple diagnostic trouble codes (DTCs) may be set due to this malfunction and during this diagnostic procedure. Complete the diagnostic procedure in order to be sure all the DTCs are diagnosed and cleared from memory.
Diagnostic Aids
* When the class 2 serial data circuit is shorted to ground, U1300 will be set. Refer to DTC U1300, U1301, or U1305 .
* When the class 2 serial data circuit is shorted to B+, U1301 will be set. Refer to DTC U1300, U1301, or U1305 .
* Disconnecting modules and turning the ignition switch to RUN may cause DTCs in the vehicle modules. Check for DTCs in each module upon completion of the required repair.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2.
A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial data circuit:
* Body Control Module (BCM)
* Electronic Brake Control Module (EBCM)
* Electronic Suspension Control (ESC)
* HVAC with CJ2
* Sensing and Diagnostic Module (SDM)
* Instrument Panel Cluster (IPC)
* Driver Door Module (DDM)
* Passenger Door Module (PDM)
* Seat Control Module (SCM) with AAB
* Powertrain Control Module (PCM)
* Radio
* Remote Control Door Lock Receiver (RCDLR)
A DTC indicating loss of communications with a particular module with a history status may be present along with a U1000 or U1255 having a current status. This indicates that the malfunction occurred when the ignition was ON.
Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
A poor connection at the star connectors will cause multiple communication DTCs to set.
An open in the class 2 serial data circuit between the DLC and one of the star connectors will prevent the scan tool from communicating with some modules. This condition will cause multiple communication DTCs to set.
This test isolates the BCM by using the J 42236 Serial Data Link Tester and a scan tool. The BCM monitors the ignition switch position and sends the appropriate power mode message to other modules. The BCM must be communicating before attempting to diagnose communication DTCs.
This test isolates each module on star connector #1 by communicating with each module separately using the J 42236 Serial Data Link Tester and a scan tool.
This test isolates each module on star connector #2 by communicating with each module separately using the J 42236 Serial Data Link Tester and a scan tool.
If there are no current DTC's that begin with a "U", the communication malfunction has been repaired.
The communication malfunction may have prevented diagnosis of the customer complaint.
Step
Action
Yes
No
1
Does the scan tool power up?
Go to Step 2
Go to Scan Tool Does Not Power Up
2
1. Turn ON the ignition with the engine OFF.
2. Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the Class 2 Message Monitor feature.
Does the scan tool communicate with any module on the class 2 serial data circuit?
Go to Step 3
Go to Step 9
3
1. Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.
Did you record any DTCs in the range of U1000 to U1305?
Go to Step 4
Go to Diagnostic Aids
4
Are the DTCs U1300, U1301 or U1305 retrieved from any module?
Go to Step 5
Go to Step 6
5
Important
Turn on the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.
Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following in Wiring Systems:
* Testing for Intermittent and Poor Connections
* Circuit Testing
* Connector Repairs
* Wiring Repairs
Did you find and correct the condition?
Go to Step 15
Go to Step 6
6
Is U1000 or U1255 the only DTC displayed in the previously specified range?
Go to DTC U1000 and U1255
Go to DTC U1001-U1254
7
1. Turn OFF the ignition.
2. Disconnect the scan tool from the data link connector (DLC).
3. Inspect for poor connections at the DLC terminals 2 and 5. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 8
8
Test the ground circuit of the DLC terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 9
9
1. Disconnect the bus bars from star connector #1 and star connector #2.
2. Inspect for poor connections at the star connectors. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 10
10
Test the class 2 serial data circuit for an open or a short between the DLC connector and the star connectors. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Control Module References in Body Control System for the applicable Diagnostic System Check
Go to Step 11
11
1. Turn OFF the ignition.
2. Install a scan tool.
3. Disconnect the bus bars from star connector #1 and star connector #2.
4. Connect J 42236 Serial Data Link Tester to both star connectors.
Important
Ensure the vehicle star connector #1 and star connector #2 correctly correspond with the Serial Data Link Tester connector #1 and connector #2. Refer to Data Link Connector (DLC) Schematics .
5. Place the switch located on the Serial Data Link Tester in the STAR CONNECTOR #1 position.
6. Rotate the rotary switch to the (M) position.
7. Turn ON the ignition with the engine OFF.
8. Attempt to communicate with the BCM.
Does the scan tool communicate with the BCM?
Go to Step 12
Go to Step 14
12
1. Place the switch located on the Serial Data Link Tester to the STAR CONNECTOR #1 position.
2. Use a scan tool and attempt to communicate with each of the following systems by rotating the rotary switch on the Serial Data Link Tester in the following positions. The Tech 2 Diagnostic Circuit Check/Class 2 Message Monitor may be used to display communication status with all systems:
* (L) = HVAC with CJ2
* (J) = RCDLR
* (H) = ESC
* (G) = IPC
* (F) = SDM
* (E) = EBCM
* (D) = RADIO
* (B) = PCM
Does the scan tool communicate with all of the systems?
Go to Step 13
Go to Step 14
13
1. Place the switch located on the Serial Data Link Tester to the STAR CONNECTOR #2 position.
2. Use a scan tool and attempt to communicate with each of the following systems by rotating the rotary switch on the Serial Data Link Tester in the following positions. The Tech 2 Diagnostic Circuit Check/Class 2 Message Monitor may be used to display communication status with all systems:
* (C) = DDM
* (D) = PDM
* (K) = SCM (with AAB
Does the scan tool communicate with all of the systems?
Go to Step 17
Go to Step 14
14
1. Turn OFF the ignition.
2. Disconnect the module that is not communicating.
3. Test the class 2 serial data circuit between the star connector and the module that is not communicating for a short to ground or a short to voltage. Turn ON the ignition with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 17
Go to Step 15
15
Inspect for poor connections at the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 17
Go to Step 16
16
Important
Perform the set up procedure for module if required.
Replace the module which is not communicating. Refer to Control Module References in Body Control System.
Did you complete the replacement?
Go to Step 17
--
17
1. Reconnect all of the disconnected modules.
2. Reconnect any other disconnected connectors.
3. Install a scan tool.
4. Turn ON the ignition with the engine OFF.
5. Wait for 10 seconds.
6. The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn OFF or disconnect the scan tool prior to performing this test. Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
7. Record all of the displayed DTCs and the DTC status.
Did you record any DTCs which begin with a "U" and with a current status?
Go to Step 19
Go to Step 18
18
Did you record any DTCs which do not begin with a "U"?
Go to Step 19
Go to Step 21
19
Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to Control Module References in Body Control System for the applicable Diagnostic System Check.
Did you complete the action?
Go to Step 20
--
20
Did you diagnose all of the DTCs?
Go to Step 21
Go to Step 19
21
Use the scan tool in order to clear the DTCs.
Did you complete the action?
System OK
--
Last edited by DeeGee; Jul 20, 2010 at 03:25 AM.
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Heres the link for Bills Current Draw Test. Go to Post #9:
http://forums.corvetteforum.com/show...rent+draw+test
And here's the thread on how to check the door hinge connections:
http://forums.corvetteforum.com/c5-t...g-on-door.html
Wish I could give you a definitive answer but hope this helps
http://forums.corvetteforum.com/show...rent+draw+test
And here's the thread on how to check the door hinge connections:
http://forums.corvetteforum.com/c5-t...g-on-door.html
Wish I could give you a definitive answer but hope this helps
Thread Starter
Heel & Toe
Joined: Jul 2010
Posts: 24
Likes: 0
From: Goodlettsville TN
I think I might have a friend who knows someone who has a Tech II at his shop. I have already taken this car to the dealership when this first started happening and they wouldn't even hook it up to the Tech II but instead told me immediately that I needed to replace the BCM and pay them the $1900 for the actual BCM and to install it. Needless to say, I told them no thanks. I have tried several of the things that Bill has said in previous forums. I can't get him to reply back to me on forums or by private PM. I messed around with the star connectors earlier tonight. I disassembled the star connector with four wires going to it, jumped to light green and dark green wire together, and still the same problems. I am going to use a OHM meter to test the resistance of each wire going to ground from the star connector tomorrow. I really appreciate all the help. I guess I am just going to have to go somewhere that I can get it hooked up to a Tech II.
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
I think I might have a friend who knows someone who has a Tech II at his shop. I have already taken this car to the dealership when this first started happening and they wouldn't even hook it up to the Tech II but instead told me immediately that I needed to replace the BCM and pay them the $1900 for the actual BCM and to install it. Needless to say, I told them no thanks. I have tried several of the things that Bill has said in previous forums. I can't get him to reply back to me on forums or by private PM. I messed around with the star connectors earlier tonight. I disassembled the star connector with four wires going to it, jumped to light green and dark green wire together, and still the same problems. I am going to use a OHM meter to test the resistance of each wire going to ground from the star connector tomorrow. I really appreciate all the help. I guess I am just going to have to go somewhere that I can get it hooked up to a Tech II.
Did you check the door hinge connectors?
Thread Starter
Heel & Toe
Joined: Jul 2010
Posts: 24
Likes: 0
From: Goodlettsville TN
The connectors I checked in the doors were the ones in the accordian tubes. I put the liquid electrical tape on those like Bill had said to do in a forum he had. Are there more connectors in the door hinges besides these?
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
What confuses me is there are only 2 connections on the IPC. It's almost plug and play so it's hard to see why you'd suddenly hit problems. I guess its all pointing towards BCM isn't it?
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Thread Starter
Heel & Toe
Joined: Jul 2010
Posts: 24
Likes: 0
From: Goodlettsville TN
It is appearing that way, but I really don't want it to be...lol.... Why I keep leaning to the idea that it is not the BCM is because I have seen several posts and Bill even said himself that if the car was reading a lot of U1064 codes and loss of communication codes that it was not the BCM is likely the serial bus wire ground somewhere or the accordian tubes in the doors. Do you think it would be worth it to take out the entire interior including carpet, all panels, seats, and everything to check for pinched wires or a loose ground? I have checked the most prone ones to cause the problems but not every single one in the car.
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
It is appearing that way, but I really don't want it to be...lol.... Why I keep leaning to the idea that it is not the BCM is because I have seen several posts and Bill even said himself that if the car was reading a lot of U1064 codes and loss of communication codes that it was not the BCM is likely the serial bus wire ground somewhere or the accordian tubes in the doors. Do you think it would be worth it to take out the entire interior including carpet, all panels, seats, and everything to check for pinched wires or a loose ground? I have checked the most prone ones to cause the problems but not every single one in the car.
It's bad that the dealer won't even run some diagnostics to tie down where the problem lies. If he ran the Tech 2 and it identifies one particular module, at least you could start troubleshooting that circuit. Bad grounds can cause this stuff so I'd check those for corrosion. The AC can leak on the carpet on the passenger side. I'd check to see if thats wet as the computer is down under the footwell panel.
Last edited by DeeGee; Jul 20, 2010 at 06:21 AM.
Thread Starter
Heel & Toe
Joined: Jul 2010
Posts: 24
Likes: 0
From: Goodlettsville TN
The wetness around the BCM was one of the first things I checked. Everything is dry and perfect as can be. I am really crossing my fingers that when I check the ohms at the star connector grounds that it will show something. I can only hope at least!
Thread Starter
Heel & Toe
Joined: Jul 2010
Posts: 24
Likes: 0
From: Goodlettsville TN
Well today I think I might have made some progress. I have read several different forums on how to check the star connectors for low resistance and so forth. I checked the DLC pin #2 purple wire and the DLC pin #4 black wire with an OHM meter. It read 00.0. I then checked the star connectors with the OHM on the connector with the most wire's.These were the readings:
Light green-18.89m
White-37.8K
Pink-OL (nothing)
Blue wire with white stripe-OL (nothing)
Grey-134.9K
Blue-10.70K
Light Blue-109.5K
Orange-18.37m
Dark Green-OL (nothing)
Purple-OL nothing.
I then checked the star connector with only four wires and got these readings:
Purple-nothing
Brown-18.5m
Light Brown-16.76m
Brown white strip-nothing
I did notice on the star connector with 4 wires that the brown white striped wire had been pinched at some point. Its not real bad though. I can't see any wire exposed but something did pinch it. I also took the drivers seat back out and didn't find anything wrong.
I also rechecked the battery today and got these readings.
12.36 with key OFF
12.17 with key ON
14.42 with car RUNNING
I am supposing that I do have a problem of some kind since several of the wires were not having any readings. I am going to post below the forum I found and went by that was testing all these wires so you will have some idea.
Here is BlackZ06's post I went by:
Troubleshooting info for the C5 serial-data-bus : (by ersatz928)
Every module which talks on the serial bus has it own piece of wire which comes to a"star" junction. The star junction is where all the wires connect together, so all the modules can talk to each other. There are actually physically two star junctions, located next to each other, to the left of the BCM module. There are two because GM needed more wire connections than one star junction block could handle, there is a short wire that connects the two star blocks together. Each star is a black (or grey?) rectangular plastic block, with lots of wires on one side. It is really just a multipin connector which is plugged-into a shorting socket, which connects all the wires together.
C5 modules (and the databus wire color) on the serial-bus are :
BCM (Light Green)
PCM (Dark Green)
IPC Instrument Cluster (Gray)
DDM Driver Door Lock Module (also controls the window) (Brown)
PDM Passenger Door Lock Module (also controls the window) (Tan)
Radio (but not the CD Changer) (Orange)
Auto-Climate control head-unit/display (Option) (White)
RCDLR (Radio receiver for the Key-Fob transmitter and Tire Pressure sensors) (Pink)
SCM module for Memory Power Seats and telescope colum (Option) (Brown white stripe)
ESC Electronic suspension shock damping control module (Option) (Dark Blue with white stripe)
EBCM Traction Control/AH module (Light Blue)
SDM (Airbag control) module (Dark Blue)
The Star Bus also has a connection at the Data Link Connector (under the drivers side dash) where you connect a OBD2 code scanner to. DLC pin #2 (Purple wire)
There are three kinds of failures that can take down the whole data-bus :
1) One of the wires is shorted to ground, somewhere along its length between the star junction and the module location.
2) One of the modules has an internal bus-driver/receiver failure which forces a continious positive voltage on the bus.
3) One of the modules has an internal bus-driver/receiver failure which forces a continious low voltage (short to ground) on the bus.
This troubleshooting assumes there is only one shorting problem with the data bus wiring, or one module.
1) Disconnect the battery
2) Use an Ohm-meter (DVM, DMM, VOM..) to measure the resistance between DLC pin #2 (Purple wire, upper row, the pin to the left of the rightmost pin), and to chassis ground DLC pin #4 (Black wire, upper row, fourth pin to the left of rightmost pin). I think the measured resistance should be 5K (5000) Ohms or greater. If it measures at least 5000 ohms, you don’t have a short-to-ground on the data bus. If it is less than 5000 ohms got the next step. NOTE : I need to verify the 5000 Ohm go/nogo resistance.
3) Unplug the 2 BCM connectors. If the low resistance goes to 5000 ohms, the problem is internal to the BCM module, replace it. If the low resistance remains, re-install the BCM connectors and goto the next step.
4) Unplug the shorting socket from both Star connectors. Use your ohmeter to probe one wire at a time, to find the low resistance to ground. Identify the offending bus-wire and/or module by using the wire color associated with each module (see the module list above). 5)Find and unplug the module you identified in step 4. If the low resistance goes away, then that module has an internal short. If the resistance stays low, then the short is in the wire itself, somewhere between the Star block and the module location.
Note : The wire colors are from my 2001 factory service manual, I have not verified that they are the correct colors at the star connector blocks , or if they apply to all model year C5s.
Any ideas?
Thanks Jamie
Light green-18.89m
White-37.8K
Pink-OL (nothing)
Blue wire with white stripe-OL (nothing)
Grey-134.9K
Blue-10.70K
Light Blue-109.5K
Orange-18.37m
Dark Green-OL (nothing)
Purple-OL nothing.
I then checked the star connector with only four wires and got these readings:
Purple-nothing
Brown-18.5m
Light Brown-16.76m
Brown white strip-nothing
I did notice on the star connector with 4 wires that the brown white striped wire had been pinched at some point. Its not real bad though. I can't see any wire exposed but something did pinch it. I also took the drivers seat back out and didn't find anything wrong.
I also rechecked the battery today and got these readings.
12.36 with key OFF
12.17 with key ON
14.42 with car RUNNING
I am supposing that I do have a problem of some kind since several of the wires were not having any readings. I am going to post below the forum I found and went by that was testing all these wires so you will have some idea.
Here is BlackZ06's post I went by:
Troubleshooting info for the C5 serial-data-bus : (by ersatz928)
Every module which talks on the serial bus has it own piece of wire which comes to a"star" junction. The star junction is where all the wires connect together, so all the modules can talk to each other. There are actually physically two star junctions, located next to each other, to the left of the BCM module. There are two because GM needed more wire connections than one star junction block could handle, there is a short wire that connects the two star blocks together. Each star is a black (or grey?) rectangular plastic block, with lots of wires on one side. It is really just a multipin connector which is plugged-into a shorting socket, which connects all the wires together.
C5 modules (and the databus wire color) on the serial-bus are :
BCM (Light Green)
PCM (Dark Green)
IPC Instrument Cluster (Gray)
DDM Driver Door Lock Module (also controls the window) (Brown)
PDM Passenger Door Lock Module (also controls the window) (Tan)
Radio (but not the CD Changer) (Orange)
Auto-Climate control head-unit/display (Option) (White)
RCDLR (Radio receiver for the Key-Fob transmitter and Tire Pressure sensors) (Pink)
SCM module for Memory Power Seats and telescope colum (Option) (Brown white stripe)
ESC Electronic suspension shock damping control module (Option) (Dark Blue with white stripe)
EBCM Traction Control/AH module (Light Blue)
SDM (Airbag control) module (Dark Blue)
The Star Bus also has a connection at the Data Link Connector (under the drivers side dash) where you connect a OBD2 code scanner to. DLC pin #2 (Purple wire)
There are three kinds of failures that can take down the whole data-bus :
1) One of the wires is shorted to ground, somewhere along its length between the star junction and the module location.
2) One of the modules has an internal bus-driver/receiver failure which forces a continious positive voltage on the bus.
3) One of the modules has an internal bus-driver/receiver failure which forces a continious low voltage (short to ground) on the bus.
This troubleshooting assumes there is only one shorting problem with the data bus wiring, or one module.
1) Disconnect the battery
2) Use an Ohm-meter (DVM, DMM, VOM..) to measure the resistance between DLC pin #2 (Purple wire, upper row, the pin to the left of the rightmost pin), and to chassis ground DLC pin #4 (Black wire, upper row, fourth pin to the left of rightmost pin). I think the measured resistance should be 5K (5000) Ohms or greater. If it measures at least 5000 ohms, you don’t have a short-to-ground on the data bus. If it is less than 5000 ohms got the next step. NOTE : I need to verify the 5000 Ohm go/nogo resistance.
3) Unplug the 2 BCM connectors. If the low resistance goes to 5000 ohms, the problem is internal to the BCM module, replace it. If the low resistance remains, re-install the BCM connectors and goto the next step.
4) Unplug the shorting socket from both Star connectors. Use your ohmeter to probe one wire at a time, to find the low resistance to ground. Identify the offending bus-wire and/or module by using the wire color associated with each module (see the module list above). 5)Find and unplug the module you identified in step 4. If the low resistance goes away, then that module has an internal short. If the resistance stays low, then the short is in the wire itself, somewhere between the Star block and the module location.
Note : The wire colors are from my 2001 factory service manual, I have not verified that they are the correct colors at the star connector blocks , or if they apply to all model year C5s.
Any ideas?
Thanks Jamie
