A bad Body Control Module (BCM) can have several symptoms related to electrical problems in a vehicle.
This includes any of the components that the BCM controls and manages such as the radio, electric windows, windshield wipers, and more.
What is a Body Control Module?
The body control module (BCM) is a computer that monitors and controls electronics located in the body of the vehicle.
Electronics located in the body of the vehicle include power windows, power mirrors, HVAC system, immobilizer system, central locking, lights, horn, wipers, and more.
The BCM also communicates with other on-board computer modules, such as the ECM.
Symptoms of a Bad Body Control Module (BCM)
- Electrical Components Don’t Work or Work Erratically
- Dashboard Warning Lights
- Battery Keeps Draining
- Failure in Driver Assist Systems
- Communication Failure Codes (U0140)
They may also work erratically, with some components turning on and off randomly.
For example, the inside dome light may work intermittently or the horn may work but then stop.
This includes warning lights such as the immobilizer, traction control, engine, ABS, and more.
It can vary which lights are displayed depending on which circuits are damaged.
If you have other symptoms along with a battery constantly draining, the BCM may have failed.
Many modern vehicles have driver assist systems that can be disabled or work intermittently.
Often, the symptoms will go off and display lights on the dashboard.
Communication codes are a sure sign there is an issue with the vehicle’s computer modules.
Things to Check with a Suspected Failed Body Control Module
- Check the Battery and Alternator are Good
- Check Fuses
- Check BCM Ground Wire
- Check Wire Harness for Damage
- Check for Brunt Smell Around BCM
Like all computers, a bad power supply can cause issues.
The fuse location will vary depending on the vehicle’s make and model.
It can be a good idea to check or test all the computer modules related to fuses or anything labeled PCM, ECM, ECU, or BCM.
A ground wire goes to all the computer modules, which must have good contact.
The ground wire to the BCM can be checked and tested.
A temporary wire, such as alligator clips, can be used to see if the unit has bad ground and if the error clears.
Connectors can also be loose or need to be re-seated to make a good contact.
A wiring issue can cause the same symptoms as a bad BCM and should be tested first before replacing the module.
If the Body Control Module has a burning smell, it likely is bad.
The unit can be opened to see if there is any burnt spot to verify it has gone bad.
Real Life Shop Example of a Bad Body Control Module (BCM)
There were several dashboard warning lights, the windows would not roll down, the interior lights flickered unpredictably, and the remote key fob had become unreliable.
Connecting a diagnostic tool to the OBDII port, the code “U0140 Lost Communication With Body Control Module” was displayed.
The symptoms and the code pointed to an issue with the Body Control Module.
The customer was concerned about the repair cost, but the vehicle was not driveable in its condition.
There was no battery or charging issue with the car, and the customer stated that the engine started and ran well.
Each computer module fuse was checked and tested, and no bad fuses were found.
All the wiring connections to the BCM were also examined and did not have any obvious damage.
A temporary ground wire was used to ground the BCM, which caused all the lights on the dashboard to go off.
The code was cleared and did not immediately come back.
A new ground wire was attached to the Body Control Module, which solved the issue.
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