DBLX

Here are my codes:
10-PCM - Powertrain Control Module
P0420 TWC System Low Efficiency Bank 1

28-TCS - Traction Control System
C1255 EBTCM Internal Malfunction

60-IPC - Instrument Panel Cluster
U1255 Serial Data Line Malfunction

B0-RFA - Remote Function Actuation
U1016 Loss of Communication with PCM
U1064 Loss of Communication with BCM
U1096 Loss of Communication with IPC

Car status; Did a full Dynatech exhaust install. Aftermarket radio. Everything else is stock. Is anyone of them serious? How do I correct them?

TIA,
Malcolm

Bill Dearborn

The exhaust may have something to do with the first code and the radio may have something to do with the third code. The second code is an ABS system code and could mean your EBCM is shot. The others are communication codes that show up when a module misses one of the periodic inter module communication exchanges. Most of the time the U codes are nothing to worry about.

However, as most of these codes could be related to a voltage supply problem I would start with checking battery voltage for proper levels and checking ground circuits for corrosion. Here are service procedures from the 2003 Service Manual. The probably are the same for 01 through 04 but could be different for 97 through 00.

DTC P0420 or P0430

Circuit Description
In order to maintain low emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), the engine controls system uses a 3-way catalytic converter. The catalyst within the converter promotes a chemical reaction, which oxidizes the HC and CO that are present in the exhaust gas. This reaction converts these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting NOx into nitrogen. The powertrain control module (PCM) monitors this process using heated oxygen sensor (HO2S) bank 1 sensor 2. HO2S bank 1 sensor 2, located in the exhaust stream past the 3-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalyst's ability to effectively convert the exhaust emissions. If the catalyst is functioning correctly, the HO2S bank 1 sensor 2 signal will be far less active than the signal that is produced by HO2S bank 1 sensor 1. This indicates that the 3-way catalytic converter's oxygen storage capacity is below an acceptable threshold.
The PCM performs this diagnostic during idle. When the conditions for running this DTC are met, the following conditions occurs:
1. The PCM captures the current rear HO2S rich-to-lean status.
2. The air-to-fuel ratio transitions from rich to lean or from lean to rich, depending on the capture rear HO2S rich-to-lean status.
3. The air-to-fuel ratio transitions a second time opposite the first air-to-fuel ratio transition.
4. The PCM captures the response time of the front and rear heated oxygen sensors when the air-to-fuel ratio transitions occur. The HO2S response time goes from less 300 mV to more than 600 mV, and from more than 600 mV to less than 300 mV.
5. The PCM measures the time it takes the rear HO2S voltage to cross a reference rich-to-lean threshold, minus the time it takes the front HO2S voltage to cross the same rich-to-lean threshold. The difference between the front HO2S time and the rear HO2S time is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.

Conditions for Running the DTC
• DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0200, P0300, P0325, P0327, P0335, P0336, P0341, P0342, P0343, P0351-P0358, P0410, P0440, P0502, P0503, P0506, P0507, P0606, P1120, P1133, P1134, P1153, P1154, P1220, P1336, P1415, P1416, or P1441 are not set.
• The intake air temperature (IAT) is more than -7°C (19°F), but less than 75°C (167°F).
• The barometric pressure (BARO) is more than 74 kPa (10.7 psi).
• The engine is operating.
• The engine coolant temperature (ECT) is more than 75°C (167°F), but less than 117°C (243°F).
• Since the end of the last idle period, the engine speed is more than 850 RPM for a minimum of:
o 17 seconds for manual transmissions
o 27 seconds for automatic transmissions
• The Closed Loop fuel control is enabled.

Conditions for Setting the DTC
The PCM determines if oxygen storage capability of the catalytic converter has degraded to less than a calibrated threshold.

Action Taken When the DTC Sets
• The malfunction indicator lamp (MIL) is turned ON.
• A DTC is stored in memory.
• The Freeze Frame/Failure Records are stored.
• The Failure Records are updated after the first failure of each ignition cycle.

Conditions for Clearing the MIL/DTC
• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and the DTC with a scan tool.

Test Description
The number below refers to the step number on the diagnostic table.
4. Before you replace the 3-way catalytic converter, correct any conditions which may have damaged the catalyst.
Step Action Yes No
1 Did you perform the Diagnostic System Check-Engine Controls? Go to Step 2
Go to Diagnostic System Check - Engine Controls

2 Are any other DTCs set? Go to the applicable DTC table Go to Step 3

3 Check for the following conditions:
• Verify that the 3-way catalytic converter is an original equipment part.
• Inspect the 3-way catalytic converter for damage from the following conditions:
o Dents
o Severe discoloration caused by excessive temperatures
o Holes
o Other conditions
• Ensure that an internal 3-way catalytic converter rattle that is caused by a damaged catalyst is not present.
• Inspect the exhaust system for the following conditions:
o Leaks
o Damage
o Loose hardware
o Missing hardware
• Ensure that the HO2S 1 and the HO2S 2 are secure, and ensure that the pigtails and the wiring are not damaged or contacting the exhaust.
Did you find and correct the condition? Go to Step 5
Go to Step 4

4
Replace the catalytic converter. Refer to Catalytic Converter Replacement in Engine Exhaust.
Is the action complete? Go to Step 5
--
5 1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? Go to Step 2
Go to Step 6

6 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed? Go to Diagnostic Trouble Code (DTC) List
System OK

DTC C1255 or C1256

Circuit Description
This DTC identifies a malfunction within the electronic brake control module (EBCM).

Conditions for Running the DTC
The ABS conditions and the braking conditions are normal.

Conditions for Setting the DTC
An internal EBCM malfunction exists.

Action Taken When the DTC Sets
C1255
If equipped, the following actions occur:
• The EBCM disables the DRP/ABS/TCS/VSES for the duration of the ignition cycle.
• The ABS indicator turns ON.
• The Traction Control and Active Handling indicator turns ON.
• The red Brake warning indicator turns ON.
• The DIC displays the following messages:
o Service ABS
o Service Traction System
o Service Active Handling
• The EBCM will also set DTC C1248.
• For some DTC C1255xx, the EBCM disables the variable effort steering (VES) for the duration of the ignition cycle.
C1256
• The ABS remains functional.
• The ABS indicator remains OFF.

Conditions for Clearing the DTC
• The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
• The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids
• The scan tool displays 2 additional characters after the DTC. Take note of the 2 character code and any other DTCs that are set. The 2 character code is an engineering aid used in order to determine the cause of the internal malfunction.
• When the scan tool displays DTC C1255m3, the EBCM has not been programmed. Perform the setup procedure for the EBCM.

Test Description
The number below refers to the step number on the diagnostic table.
2. Determines whether the DTC is current.
Step Action Yes No
Schematic Reference: ABS Schematics

1 Did you perform the ABS Diagnostic System Check? Go to Step 2
Go to Diagnostic System Check - ABS

2
1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Use the scan tool in order to clear the DTCs.
4. With the scan tool, perform the Automated Test.
Does the DTC reset as a current DTC? Go to Step 3
Go to Testing for Intermittent and Poor Connections in Wiring Systems

3 Replace the EBCM. Refer to Electronic Brake Control Module (EBCM) Replacement .
Did you complete the repair? Go to Step 4
--
4 1. Use the scan tool in order to clear the DTCs.
2. With the scan tool, perform the Automated Test.
Does the DTC reset? Go to Step 2
System OK


DTC U1000 and U1255

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. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least 1 critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. The DTC will only be reported once if more than 1 critical parameter does not have a sending module identification number associated with it.
The following systems communicate on the class 2 serial data circuit:
• Body Control Module (BCM)
• Electronic Brake Control Module (EBCM)
• Electronic Suspension Control (ESC) Module
• 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)

Conditions for Running the DTC
• Voltage supplied to the module is in the normal operating voltage range.
• Diagnostic trouble codes U1300, U1301 or U1305 are not set.
• The module setting the DTC requires serial data communication to occur.

Conditions for Setting the DTC
At least 1 critical operating parameter has not been associated with an identification number within about 5 seconds after beginning serial data communication.

Action Taken When the DTC Sets
The module uses a default value for the missing parameter.

Conditions for Clearing the DTC
• A current DTC U1000 or U1255 will clear when all critical operating parameter for the module have been associated with an identification number or at the end of the current ignition cycle.
• A history DTC resets after 50 ignition switch cycles with no repeated failure.

Diagnostic Aids
When a malfunction such as an open fuse to a module occurs while modules are communicating, a current DTC is set indicating lost communication with a specific module DTC. When the modules stop communicating, ignition is turned OFF, the current Lost Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so DTC U1000 or U1255 is set as current by the other modules. If the malfunction occurs when the modules are not communicating, only DTC U1000 or U1255 is set.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
1. A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
2. The modules which is not communicating is the likely cause of U1000 or U1255 being set.
5. The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
6. The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
7. The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
11. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
13. If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
14. The module which set U1000 or U1255 is the likely cause of the malfunction.
Step Action Yes No
1
Did you record any DTCs in the range of U1001-U1254 with a history status? Go to DTC U1001-U1254
Go to Step 2

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.
3. Record all of the modules communicating on the class 2 serial data circuit.
4. Compare the list of modules which are communicating to the list given in the Circuit Description.
Does any module on the class 2 serial data circuit not communicate? Go to Step 3
Go to Step 13

3 Test the battery positive voltage circuits and the ignition voltage circuits of the module that is not communicating for an open or a short to ground. Refer to Control Module References in Body Control System for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition? Go to Step 9
Go to Step 4

4 1. Turn OFF the ignition.
2. Test the ground circuits of the module that is not communicating for an open. Refer to Control Module References in Body Control System for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition? Go to Step 9
Go to Step 5

5
1. Disconnect both star connectors.
2. Inspect for poor connection 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 Step 9
Go to Step 6

6
Test the class 2 serial data circuit of the module that is not communicating for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition? Go to Step 9
Go to Step 7

7
Inspect for poor connections at the battery positive voltage circuits, the ignition voltage circuits, the ground circuits, and 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 9
Go to Step 8

8 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 11
--
9 1. Install a scan tool.
2. Turn ON the ignition with the engine OFF.
3. Select the Display DTCs function for the module which was not communicating.
Does the scan tool display and DTCs which do not begin with a "U"? Go to Control Module References in Body Control System for the applicable Diagnostic System Check Go to Step 10

10 Use the scan tool in order to clear the DTCs.
Did you complete the action? Go to Step 11
--
11
Select the Display DTCs function for the modules which had U1000 or U1255 set as a current DTC.
Does the scan tool display any DTCs which do not begin with a "U"? Go to Control Module References in Body Control System for the applicable Diagnostic System Check Go to Step 12

12 Use the scan tool in order to clear the DTCs.
Did you complete the action? System OK --
13
Did you record any other DTCs for the modules which had U1000 or U1255 set as a current DTC? Go to Control Module References in Body Control System for the applicable Diagnostic System Check Go to Step 14

14
1. Install a scan tool.
2. Turn ON the ignition with the engine OFF.
3. Use the scan tool in order to clear the DTCs.
4. Turn OFF the ignition for at least 5 seconds.
5. Turn ON the ignition with the engine OFF.
6. Select the Display DTCs function.
Does the scan tool display U1000 or U1255 set as a current DTC? Go to Step 15
Go to Diagnostic Aids
15 Important
Perform the set up procedure for module if required.
Replace the module which had U1000 or U1255 set as a current DTC. Refer to Control Module References in Body Control System.
Did you complete the replacement? System OK


All GM Vehicles Using Class 2 Communications Diagnostic Strategy for DTC U1000 or U1255 - kw BCM code EBTCM radio RIM #PIT3154 - (Sep 10, 2004)
All GM Vehicles Using Class 2 Communications Diagnostic Strategy For DTC U1000 or U1255
.
The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Condition/Concern:
DTC U1000 or U1255 set current or history, with or without other DTCs

Recommendation/Instructions:
DTC U1000 Class 2 Data Link
DTC U1255 Lost Communications
These DTCs set when the control module does not receive a message that it was expecting from another control module, and does not know which control module did not send that message.
1. If the DTC U1000 or U1255 is set in history with other DTCs set current or history, diagnose the other DTCs first.
2. If the DTC U1000 or U1255 set current, this usually indicates a module that is currently not communicating or a configuration issue. For example, if the control module is configured for an option (ie: Onstar, Keyless Entry, Memory Mirrors, etc.) that the vehicle does not have, it may expect to receive a message regarding this missing feature. This would usually occur due to the control module being recently replaced and incorrectly setup.
3. When the DTC U1000 or U1255 is current, the module that is not communicating may not even be listed on the Tech 2 on the Diagnostic Circuit Check/Class 2 Message Monitor list.
4. If the DTC U1000 or U1255 has set in history without other DTCs, replacing the control module setting the DTC is most likely NOT the solution. The module that has set the code is looking for an input from another module that is not communicating. Since the module did not receive an input that it is expecting to see, it sets a U1000 or U1255 which indicates there was a loss of communications. Look at the customer’s complaint (ie: intermittent, erratic tachometer operation); this will probably be a better indication of the control module that is the source of the concern.
.
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

Models:
(All GM vehicles using Class 2 communications)



Bill

SpeedyZ

Like Bill said, all the U codes are communications errors. These codes are saying that a device is having trouble communication to the other device listed. In a C5 all the computers chit chat all the time to keep each other updated, if they can't communicate with someone they will set a code indicating such. These types of codes will always be set when you have a low or dead battery. As the voltage gets low things start to fail and some devices drop off line before others so the one up the longest will start setting these codes. If you left the door open too long or something like that and ran the battery down they are nothing to worry about. Simply clear them and see what comes back. If they keep returning then look into a bad battery, bad connection at batter, and then the grounding issues.