Voltage draw BCM1&IPC help please?
Thread Starter
Racer
Joined: Nov 2006
Posts: 386
Likes: 0
From: El Paso Texas
Voltage draw BCM1&IPC help please?
I forgot the technical term for whats going on but here's what's happening: Battery is going dead over night or between start of shift and end of shift at work.
Pulled battery ground and put a test light between terminal wire and post. Big draw lighting up. Pulled fuses until it went away. Ended up being 25- BCM1 & IPC.
5- Radio/CD gives me a flashing light that goes as high as 8 volts.
Is that normal? Should I just buy a new radio?
What does the BCM1 control? Is IPC Instrument Panel Cluster? How do I track down the problem?
I've been disconnecting the battery ground to avoid having to jump start, but I know there's a problem that if I don't repair, could burn down the car. I read "New Steering Wheel Position Sensor - Now car won't start" and figure fuse 25 in the footwell box has some thing to do with starting, because when I took the fuse out, I couldn't start the car and the gauges wouldn't come on.
Pulled battery ground and put a test light between terminal wire and post. Big draw lighting up. Pulled fuses until it went away. Ended up being 25- BCM1 & IPC.
5- Radio/CD gives me a flashing light that goes as high as 8 volts.
Is that normal? Should I just buy a new radio?
What does the BCM1 control? Is IPC Instrument Panel Cluster? How do I track down the problem?
I've been disconnecting the battery ground to avoid having to jump start, but I know there's a problem that if I don't repair, could burn down the car. I read "New Steering Wheel Position Sensor - Now car won't start" and figure fuse 25 in the footwell box has some thing to do with starting, because when I took the fuse out, I couldn't start the car and the gauges wouldn't come on.
Tech Contributor
Joined: Oct 1999
Posts: 41,013
Likes: 9,773
From: Charlotte, NC (formerly Endicott, NY)
The BCM monitors power draw of the various modules in the car for up to 15 minutes and then turns off any loads.
Here is a description of the BCM activity:
Body Control System Description and Operation
This vehicle is equipped with a Body Control Module (BCM) capable of performing multiple body control functions. The BCM, which is the power mode master, is responsible for sending the power mode messages on the serial data line to other systems.
Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the Body Control Module (BCM). The PMM receives two signals/circuits from the ignition switch. These are the Ignition 1and Ignition 2 ignition switch signals/circuits.
To determine the correct power mode the PMM uses:
The state of these signals/circuits, either switch closed (B+ = 1) or switch open (B+ = 0)
The sequence of switch closures received by the PMM
The status of the engine run flag
Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the PMM fail to send a power mode message. The fail-safe plan covers those modules using exclusively serial data control of power mode as well as those modules with discrete ignition signal inputs.
Serial Data Messages
The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid PMM message until they can check for the engine run flag status on the serial data circuits. If the PMM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to "RUN". In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
On this vehicle the following modules receive Serial Data Messages for power mode status:
Driver Door Module (DDM)
Passenger Door Module (PDM)
Radio
Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid PMM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, B+, the modules will fail-safe to the "RUN" power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
BCM Wake-up/Sleep States
The BCM is able to control or perform all of the BCM functions in the wake-up state. The BCM enters the sleep state when active control or monitoring of system functions has stopped, and the BCM has become idle again. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors for these inputs during the sleep state, where the BCM is able to detect switch transitions that cause the BCM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense both the insertion of the ignition key and the power mode requested. This would allow the BCM to enter a sleep state when the key is IN or OUT of the ignition.
The BCM will enter a wake-up state if any of the following wake-up inputs are detected:
Any activity on the serial data line
Hatch ajar switch
Hatch release switch
Door ajar switch
Key-in-ignition switch
Monitored load relay
Park/fog/headlamps are on
The BCM experiences a battery disconnect and reconnect condition.
The ignition is turned ON.
The BCM will enter a sleep state when all of the following conditions exist:
No activity exists on the serial data line.
The ignition switch is OFF.
No outputs are commanded.
No delay timers are actively counting.
No wake-up inputs are present.
If all these conditions are met the BCM will enter a low power or sleep condition. This condition indicates that the BCM, which is the power mode master of the vehicle, has sent an OFF-ASLEEP message to the other systems on the serial data line.
Power Requirements
The BCM has two main power feeds (high and low current), and two main grounds. The low power feed (battery 1) is used to provide power for the BCMs logic and internal driver operation. The high power feed (battery 2) is used to provide power for systems that draw higher amounts of current (motors, lights, etc.). The BCM will operate properly with a system voltage of 9.0-16.0 volts. If system voltages exceed 16.0 volts the BCM will provide protection by disabling certain functions that may be damaged due to higher than normal system voltages.
Monitored Loads
In order to minimize any battery rundown, the BCM can detect if certain electrical loads have been left ON after the ignition is turned OFF and the driver has left the vehicle. When the BCM detects that the ignition has been cycled to the OFF position, the BCM immediately checks the status of the load monitor input. If the BCM detects that a load is present (grounded input), the BCM turns ON the load monitor relay for 15 minutes. If after 15 minutes the BCM still recognizes that a load is present, the BCM will turn OFF the relay, removing the battery voltage from the loads. The BCM continues to monitor this circuit for a switch transition. The BCM will again turn ON the relay for 15 minutes if a switch transition occurs.
Load Shed Control
The BCM can turn off the rear window defogger and heated outside mirror electrical loads when the vehicle is in a condition where these loads may discharge the battery. The BCM will also remove these loads when engine demands are greater.
Interior Lamp Over Voltage Protection
The BCM disables the interior lamp bulbs when the system voltage is above 18.0 volts in order to extend the bulb life.
Driver in Vehicle Detection
Using the ignition switch/door ajar inputs, the BCM can detect whether or not the driver has left the vehicle. If the ignition is turned to OFF with no door ajar status detected, the BCM assumes that the driver is in the vehicle. As soon as the BCM detects a door ajar, the BCM will assume the driver has left the vehicle. The BCM uses this information to determine the RAP status, then sends the status to the other systems also responsible for RAP functions.
BCM Fail-Soft Condition
If a particular BCM malfunction would result in unacceptable system operation, the BCM takes a fail-soft action in order to minimize the condition. A typical fail-soft action would be the substitution of a fixed input or output value when the BCM is unable to interpret data correctly.
If you have a current draw issue I would first investigate whether there is a problem with one of the relays that control the monitored system loads. If the relay is shorted the load cannot be removed and the monitored module may run the battery down. If the relays all work OK then the BCM control line for a relay may be keeping the relay activated which could mean you have a bad BCM.
Bill
Here is a description of the BCM activity:
Body Control System Description and Operation
This vehicle is equipped with a Body Control Module (BCM) capable of performing multiple body control functions. The BCM, which is the power mode master, is responsible for sending the power mode messages on the serial data line to other systems.
Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the Body Control Module (BCM). The PMM receives two signals/circuits from the ignition switch. These are the Ignition 1and Ignition 2 ignition switch signals/circuits.
To determine the correct power mode the PMM uses:
The state of these signals/circuits, either switch closed (B+ = 1) or switch open (B+ = 0)
The sequence of switch closures received by the PMM
The status of the engine run flag
Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the PMM fail to send a power mode message. The fail-safe plan covers those modules using exclusively serial data control of power mode as well as those modules with discrete ignition signal inputs.
Serial Data Messages
The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid PMM message until they can check for the engine run flag status on the serial data circuits. If the PMM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to "RUN". In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
On this vehicle the following modules receive Serial Data Messages for power mode status:
Driver Door Module (DDM)
Passenger Door Module (PDM)
Radio
Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid PMM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, B+, the modules will fail-safe to the "RUN" power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
BCM Wake-up/Sleep States
The BCM is able to control or perform all of the BCM functions in the wake-up state. The BCM enters the sleep state when active control or monitoring of system functions has stopped, and the BCM has become idle again. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors for these inputs during the sleep state, where the BCM is able to detect switch transitions that cause the BCM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense both the insertion of the ignition key and the power mode requested. This would allow the BCM to enter a sleep state when the key is IN or OUT of the ignition.
The BCM will enter a wake-up state if any of the following wake-up inputs are detected:
Any activity on the serial data line
Hatch ajar switch
Hatch release switch
Door ajar switch
Key-in-ignition switch
Monitored load relay
Park/fog/headlamps are on
The BCM experiences a battery disconnect and reconnect condition.
The ignition is turned ON.
The BCM will enter a sleep state when all of the following conditions exist:
No activity exists on the serial data line.
The ignition switch is OFF.
No outputs are commanded.
No delay timers are actively counting.
No wake-up inputs are present.
If all these conditions are met the BCM will enter a low power or sleep condition. This condition indicates that the BCM, which is the power mode master of the vehicle, has sent an OFF-ASLEEP message to the other systems on the serial data line.
Power Requirements
The BCM has two main power feeds (high and low current), and two main grounds. The low power feed (battery 1) is used to provide power for the BCMs logic and internal driver operation. The high power feed (battery 2) is used to provide power for systems that draw higher amounts of current (motors, lights, etc.). The BCM will operate properly with a system voltage of 9.0-16.0 volts. If system voltages exceed 16.0 volts the BCM will provide protection by disabling certain functions that may be damaged due to higher than normal system voltages.
Monitored Loads
In order to minimize any battery rundown, the BCM can detect if certain electrical loads have been left ON after the ignition is turned OFF and the driver has left the vehicle. When the BCM detects that the ignition has been cycled to the OFF position, the BCM immediately checks the status of the load monitor input. If the BCM detects that a load is present (grounded input), the BCM turns ON the load monitor relay for 15 minutes. If after 15 minutes the BCM still recognizes that a load is present, the BCM will turn OFF the relay, removing the battery voltage from the loads. The BCM continues to monitor this circuit for a switch transition. The BCM will again turn ON the relay for 15 minutes if a switch transition occurs.
Load Shed Control
The BCM can turn off the rear window defogger and heated outside mirror electrical loads when the vehicle is in a condition where these loads may discharge the battery. The BCM will also remove these loads when engine demands are greater.
Interior Lamp Over Voltage Protection
The BCM disables the interior lamp bulbs when the system voltage is above 18.0 volts in order to extend the bulb life.
Driver in Vehicle Detection
Using the ignition switch/door ajar inputs, the BCM can detect whether or not the driver has left the vehicle. If the ignition is turned to OFF with no door ajar status detected, the BCM assumes that the driver is in the vehicle. As soon as the BCM detects a door ajar, the BCM will assume the driver has left the vehicle. The BCM uses this information to determine the RAP status, then sends the status to the other systems also responsible for RAP functions.
BCM Fail-Soft Condition
If a particular BCM malfunction would result in unacceptable system operation, the BCM takes a fail-soft action in order to minimize the condition. A typical fail-soft action would be the substitution of a fixed input or output value when the BCM is unable to interpret data correctly.
If you have a current draw issue I would first investigate whether there is a problem with one of the relays that control the monitored system loads. If the relay is shorted the load cannot be removed and the monitored module may run the battery down. If the relays all work OK then the BCM control line for a relay may be keeping the relay activated which could mean you have a bad BCM.
Bill
Last edited by Bill Dearborn; Apr 5, 2008 at 11:43 PM.
Thread Starter
Racer
Joined: Nov 2006
Posts: 386
Likes: 0
From: El Paso Texas
I removed all the relays in the fuse box in the passener foot well and still had the test light shine bright. Is there a relay controlled by the BCM1 in the battery box fuse box?
Should I remove them all from the battery box fuse box too?
I just read through that other post about loose female pins and bad grounds. Could it be one of those porblems?
Should I remove them all from the battery box fuse box too?
I just read through that other post about loose female pins and bad grounds. Could it be one of those porblems?
Last edited by Castrellon; Apr 6, 2008 at 06:20 PM.
Thread Starter
Racer
Joined: Nov 2006
Posts: 386
Likes: 0
From: El Paso Texas
The BCM will enter a wake-up state if any of the following wake-up inputs are detected:
Any activity on the serial data line
Hatch ajar switch
Hatch release switch
Door ajar switch
Key-in-ignition switch
Monitored load relay
Park/fog/headlamps are on
The BCM experiences a battery disconnect and reconnect condition.
The ignition is turned ON.
The BCM will enter a sleep state when all of the following conditions exist:
No activity exists on the serial data line.
The ignition switch is OFF.
No outputs are commanded.
No delay timers are actively counting.
No wake-up inputs are present.
Any activity on the serial data line
Hatch ajar switch
Hatch release switch
Door ajar switch
Key-in-ignition switch
Monitored load relay
Park/fog/headlamps are on
The BCM experiences a battery disconnect and reconnect condition.
The ignition is turned ON.
The BCM will enter a sleep state when all of the following conditions exist:
No activity exists on the serial data line.
The ignition switch is OFF.
No outputs are commanded.
No delay timers are actively counting.
No wake-up inputs are present.
I left one other thing that may be important. My door locks don't work, my abs trac control lights have been on almost since I baught the car in '03 and the drivers side mirror is stuck on dim (night glare). Could these all corralate?
Thread Starter
Racer
Joined: Nov 2006
Posts: 386
Likes: 0
From: El Paso Texas
pics
Can I pry back on this to get the wire harness with damaged grey wire out for more room to repair the break?
'Cause here it looks like a lot more work.
Seems to me all the clear sheathed wires from Corvettes are like this. What gives? Won't this cause a short with all 'Vettes?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Hangggggggggggggggggggg Onnnnnnnnnnnnnnnnnn!!! 
Your going about this ALL WRONG! You need to do an AMP METER test! NOT A BULB TEST!!!!!
. Your BCM is always going to draw current no matter what and make that bulb light up!
Disconnect the negative battery terminal and insert an amp meter capable of reading 10 amps between the battery and the neg cable.
The BCM controls the electrical system and monitors the security system. Once the car sits for a little over 10 min, you should see a max current draw of 20-30 MILLIAMPS. I have a really good post on all of this somewhere that explains all the CRAP that can cause this problem. Do a search with KEY WORDS current draw.
BC
Your going about this ALL WRONG! You need to do an AMP METER test! NOT A BULB TEST!!!!!
. Your BCM is always going to draw current no matter what and make that bulb light up!Disconnect the negative battery terminal and insert an amp meter capable of reading 10 amps between the battery and the neg cable.
The BCM controls the electrical system and monitors the security system. Once the car sits for a little over 10 min, you should see a max current draw of 20-30 MILLIAMPS. I have a really good post on all of this somewhere that explains all the CRAP that can cause this problem. Do a search with KEY WORDS current draw.
BC
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Thread Starter
Racer
Joined: Nov 2006
Posts: 386
Likes: 0
From: El Paso Texas
Skipped a bunch of steps and went with my gut feeling last night and removed the 5- RDO/CD fuse and it started right up this morning.
Key on engine off 12v. even. Cranking the gauge went to 9v. which is bad sign given it's 75ºF out or warmer. So, I put the charger on medium for a half hour.
Key on engine off 12v. even. Cranking the gauge went to 9v. which is bad sign given it's 75ºF out or warmer. So, I put the charger on medium for a half hour.
Thread Starter
Racer
Joined: Nov 2006
Posts: 386
Likes: 0
From: El Paso Texas
Hangggggggggggggggggggg Onnnnnnnnnnnnnnnnnn!!!
Your going about this ALL WRONG! You need to do an AMP METER test! NOT A BULB TEST!!!!! . Your BCM is always going to draw current no matter what and make that bulb light up!
Disconnect the negative battery terminal and insert an amp meter capable of reading 10 amps between the battery and the neg cable.
The BCM controls the electrical system and monitors the security system. Once the car sits for a little over 10 min, you should see a max current draw of 20-30 MILLIAMPS. I have a really good post on all of this somewhere that explains all the CRAP that can cause this problem. Do a search with KEY WORDS current draw.
BC
Your going about this ALL WRONG! You need to do an AMP METER test! NOT A BULB TEST!!!!!
. Your BCM is always going to draw current no matter what and make that bulb light up!Disconnect the negative battery terminal and insert an amp meter capable of reading 10 amps between the battery and the neg cable.
The BCM controls the electrical system and monitors the security system. Once the car sits for a little over 10 min, you should see a max current draw of 20-30 MILLIAMPS. I have a really good post on all of this somewhere that explains all the CRAP that can cause this problem. Do a search with KEY WORDS current draw.
BC
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
That will do it. Just MAKE SURE you let it time out. If everything is off, it should take 2-3 min. If you leave the hood light on, it will take 10-12 min.
When you first connect the battery it will read 8+ amps, then drop to 3-4 amps, then 1-2 amps and then sleep mode. 20-25 ish milliamps.
When you first connect the battery it will read 8+ amps, then drop to 3-4 amps, then 1-2 amps and then sleep mode. 20-25 ish milliamps.
Thread Starter
Racer
Joined: Nov 2006
Posts: 386
Likes: 0
From: El Paso Texas
Weird. I got 3.58 mA when I began the test with the radio fuse out.
Went for a walk, came back after 30 minutes or so and it was at 3.18 mA. Disconnected, shower and changed (half hour) reconnected meter and it was at 3.38 mA.
Put the fuse in and tried to cycle the key, hope that didn't hurt anything, no power to dash. Checked the meter and it was at 3.34 mA. Doors are closed, under hood bulb is out.
After ten minutes, it's at 3.13 mA. Intermitant draw? Was it the radio after all? I'm going to leave the radio fuse out when I get to work. Put it back in and check the draw again when I get home from work. Usually when I've seen GM radios go bad it keeps power going to the clock display. This one hasn't done that yet. This is driving me nuts.
Is 3.13 mA enough to kill a battery in 8.5 hours?
Went for a walk, came back after 30 minutes or so and it was at 3.18 mA. Disconnected, shower and changed (half hour) reconnected meter and it was at 3.38 mA.
Put the fuse in and tried to cycle the key, hope that didn't hurt anything, no power to dash. Checked the meter and it was at 3.34 mA. Doors are closed, under hood bulb is out.
After ten minutes, it's at 3.13 mA. Intermitant draw? Was it the radio after all? I'm going to leave the radio fuse out when I get to work. Put it back in and check the draw again when I get home from work. Usually when I've seen GM radios go bad it keeps power going to the clock display. This one hasn't done that yet. This is driving me nuts.
Is 3.13 mA enough to kill a battery in 8.5 hours?
Last edited by Castrellon; Apr 8, 2008 at 03:52 PM.
Cruising
Joined: Dec 2021
Posts: 12
Likes: 4
From: Texas
The BCM monitors power draw of the various modules in the car for up to 15 minutes and then turns off any loads.
Here is a description of the BCM activity:
Body Control System Description and Operation
This vehicle is equipped with a Body Control Module (BCM) capable of performing multiple body control functions. The BCM, which is the power mode master, is responsible for sending the power mode messages on the serial data line to other systems.
Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the Body Control Module (BCM). The PMM receives two signals/circuits from the ignition switch. These are the Ignition 1and Ignition 2 ignition switch signals/circuits.
To determine the correct power mode the PMM uses:
The state of these signals/circuits, either switch closed (B+ = 1) or switch open (B+ = 0)
The sequence of switch closures received by the PMM
The status of the engine run flag
Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the PMM fail to send a power mode message. The fail-safe plan covers those modules using exclusively serial data control of power mode as well as those modules with discrete ignition signal inputs.
Serial Data Messages
The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid PMM message until they can check for the engine run flag status on the serial data circuits. If the PMM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to "RUN". In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
On this vehicle the following modules receive Serial Data Messages for power mode status:
Driver Door Module (DDM)
Passenger Door Module (PDM)
Radio
Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid PMM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, B+, the modules will fail-safe to the "RUN" power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
BCM Wake-up/Sleep States
The BCM is able to control or perform all of the BCM functions in the wake-up state. The BCM enters the sleep state when active control or monitoring of system functions has stopped, and the BCM has become idle again. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors for these inputs during the sleep state, where the BCM is able to detect switch transitions that cause the BCM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense both the insertion of the ignition key and the power mode requested. This would allow the BCM to enter a sleep state when the key is IN or OUT of the ignition.
The BCM will enter a wake-up state if any of the following wake-up inputs are detected:
Any activity on the serial data line
Hatch ajar switch
Hatch release switch
Door ajar switch
Key-in-ignition switch
Monitored load relay
Park/fog/headlamps are on
The BCM experiences a battery disconnect and reconnect condition.
The ignition is turned ON.
The BCM will enter a sleep state when all of the following conditions exist:
No activity exists on the serial data line.
The ignition switch is OFF.
No outputs are commanded.
No delay timers are actively counting.
No wake-up inputs are present.
If all these conditions are met the BCM will enter a low power or sleep condition. This condition indicates that the BCM, which is the power mode master of the vehicle, has sent an OFF-ASLEEP message to the other systems on the serial data line.
Power Requirements
The BCM has two main power feeds (high and low current), and two main grounds. The low power feed (battery 1) is used to provide power for the BCMs logic and internal driver operation. The high power feed (battery 2) is used to provide power for systems that draw higher amounts of current (motors, lights, etc.). The BCM will operate properly with a system voltage of 9.0-16.0 volts. If system voltages exceed 16.0 volts the BCM will provide protection by disabling certain functions that may be damaged due to higher than normal system voltages.
Monitored Loads
In order to minimize any battery rundown, the BCM can detect if certain electrical loads have been left ON after the ignition is turned OFF and the driver has left the vehicle. When the BCM detects that the ignition has been cycled to the OFF position, the BCM immediately checks the status of the load monitor input. If the BCM detects that a load is present (grounded input), the BCM turns ON the load monitor relay for 15 minutes. If after 15 minutes the BCM still recognizes that a load is present, the BCM will turn OFF the relay, removing the battery voltage from the loads. The BCM continues to monitor this circuit for a switch transition. The BCM will again turn ON the relay for 15 minutes if a switch transition occurs.
Load Shed Control
The BCM can turn off the rear window defogger and heated outside mirror electrical loads when the vehicle is in a condition where these loads may discharge the battery. The BCM will also remove these loads when engine demands are greater.
Interior Lamp Over Voltage Protection
The BCM disables the interior lamp bulbs when the system voltage is above 18.0 volts in order to extend the bulb life.
Driver in Vehicle Detection
Using the ignition switch/door ajar inputs, the BCM can detect whether or not the driver has left the vehicle. If the ignition is turned to OFF with no door ajar status detected, the BCM assumes that the driver is in the vehicle. As soon as the BCM detects a door ajar, the BCM will assume the driver has left the vehicle. The BCM uses this information to determine the RAP status, then sends the status to the other systems also responsible for RAP functions.
BCM Fail-Soft Condition
If a particular BCM malfunction would result in unacceptable system operation, the BCM takes a fail-soft action in order to minimize the condition. A typical fail-soft action would be the substitution of a fixed input or output value when the BCM is unable to interpret data correctly.
If you have a current draw issue I would first investigate whether there is a problem with one of the relays that control the monitored system loads. If the relay is shorted the load cannot be removed and the monitored module may run the battery down. If the relays all work OK then the BCM control line for a relay may be keeping the relay activated which could mean you have a bad BCM.
Bill
Here is a description of the BCM activity:
Body Control System Description and Operation
This vehicle is equipped with a Body Control Module (BCM) capable of performing multiple body control functions. The BCM, which is the power mode master, is responsible for sending the power mode messages on the serial data line to other systems.
Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the Body Control Module (BCM). The PMM receives two signals/circuits from the ignition switch. These are the Ignition 1and Ignition 2 ignition switch signals/circuits.
To determine the correct power mode the PMM uses:
The state of these signals/circuits, either switch closed (B+ = 1) or switch open (B+ = 0)
The sequence of switch closures received by the PMM
The status of the engine run flag
Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the PMM fail to send a power mode message. The fail-safe plan covers those modules using exclusively serial data control of power mode as well as those modules with discrete ignition signal inputs.
Serial Data Messages
The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid PMM message until they can check for the engine run flag status on the serial data circuits. If the PMM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to "RUN". In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
On this vehicle the following modules receive Serial Data Messages for power mode status:
Driver Door Module (DDM)
Passenger Door Module (PDM)
Radio
Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid PMM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, B+, the modules will fail-safe to the "RUN" power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
BCM Wake-up/Sleep States
The BCM is able to control or perform all of the BCM functions in the wake-up state. The BCM enters the sleep state when active control or monitoring of system functions has stopped, and the BCM has become idle again. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors for these inputs during the sleep state, where the BCM is able to detect switch transitions that cause the BCM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense both the insertion of the ignition key and the power mode requested. This would allow the BCM to enter a sleep state when the key is IN or OUT of the ignition.
The BCM will enter a wake-up state if any of the following wake-up inputs are detected:
Any activity on the serial data line
Hatch ajar switch
Hatch release switch
Door ajar switch
Key-in-ignition switch
Monitored load relay
Park/fog/headlamps are on
The BCM experiences a battery disconnect and reconnect condition.
The ignition is turned ON.
The BCM will enter a sleep state when all of the following conditions exist:
No activity exists on the serial data line.
The ignition switch is OFF.
No outputs are commanded.
No delay timers are actively counting.
No wake-up inputs are present.
If all these conditions are met the BCM will enter a low power or sleep condition. This condition indicates that the BCM, which is the power mode master of the vehicle, has sent an OFF-ASLEEP message to the other systems on the serial data line.
Power Requirements
The BCM has two main power feeds (high and low current), and two main grounds. The low power feed (battery 1) is used to provide power for the BCMs logic and internal driver operation. The high power feed (battery 2) is used to provide power for systems that draw higher amounts of current (motors, lights, etc.). The BCM will operate properly with a system voltage of 9.0-16.0 volts. If system voltages exceed 16.0 volts the BCM will provide protection by disabling certain functions that may be damaged due to higher than normal system voltages.
Monitored Loads
In order to minimize any battery rundown, the BCM can detect if certain electrical loads have been left ON after the ignition is turned OFF and the driver has left the vehicle. When the BCM detects that the ignition has been cycled to the OFF position, the BCM immediately checks the status of the load monitor input. If the BCM detects that a load is present (grounded input), the BCM turns ON the load monitor relay for 15 minutes. If after 15 minutes the BCM still recognizes that a load is present, the BCM will turn OFF the relay, removing the battery voltage from the loads. The BCM continues to monitor this circuit for a switch transition. The BCM will again turn ON the relay for 15 minutes if a switch transition occurs.
Load Shed Control
The BCM can turn off the rear window defogger and heated outside mirror electrical loads when the vehicle is in a condition where these loads may discharge the battery. The BCM will also remove these loads when engine demands are greater.
Interior Lamp Over Voltage Protection
The BCM disables the interior lamp bulbs when the system voltage is above 18.0 volts in order to extend the bulb life.
Driver in Vehicle Detection
Using the ignition switch/door ajar inputs, the BCM can detect whether or not the driver has left the vehicle. If the ignition is turned to OFF with no door ajar status detected, the BCM assumes that the driver is in the vehicle. As soon as the BCM detects a door ajar, the BCM will assume the driver has left the vehicle. The BCM uses this information to determine the RAP status, then sends the status to the other systems also responsible for RAP functions.
BCM Fail-Soft Condition
If a particular BCM malfunction would result in unacceptable system operation, the BCM takes a fail-soft action in order to minimize the condition. A typical fail-soft action would be the substitution of a fixed input or output value when the BCM is unable to interpret data correctly.
If you have a current draw issue I would first investigate whether there is a problem with one of the relays that control the monitored system loads. If the relay is shorted the load cannot be removed and the monitored module may run the battery down. If the relays all work OK then the BCM control line for a relay may be keeping the relay activated which could mean you have a bad BCM.
Bill
