7 Symptoms of a Bad Body Control Module
The body control module (BCM) is a type of computer that controls many of your vehicle’s internal and external electrical systems in addition to normal engine operation. It can operate windows, headlights, taillights, fog lights, door locks, HVAC controls, and more.
If your BCM isn’t working, many of these systems will work intermittently or not at all. Here are some of the most common symptoms of a bad body control module and how much it will cost to replace it.
Symptoms of a Failed Body Control Module
1) Dead Battery
A poor electrical connection in the body control module can cause a parasitic discharge. Parasitic power draw occurs when a vehicle system draws power from the battery even when the vehicle system needs to be turned off.
If your battery dies after sitting for a day or two, it’s probably parasitic power draw. Using a multimeter, you can identify the source of parasitic power draw. Depending on your vehicle’s battery, it may be empty if left for a few weeks.
2) Buttons stop working
The body control unit receives signals from buttons and switches pressed inside the car. If some or all of the internal buttons stop working, it is an indication that the body control module is defective.
3) Blown fuse
A short circuit can create dangerous current levels in certain circuits. Fuses are designed to prevent this excess current from damaging the circuit or causing a fire.
If the fused circuit is connected to the body control module, try replacing the body control module to see if that resolves the issue. Always replace fuses with ones that are rated for the same amperage.
4) Electrical Gremlins
“Electrical Gremlins” is a colloquial term for irregular electrical problems that are often intermittent or random. Electrical gremlins are usually caused by short circuits, faulty grounds, and loose connections.
Inconsistent voltages or weak signals between expected values can cause intermittent electrical problems in a properly functioning system.
5) Emergency Mode
Body control devices often have what is called an emergency drive feature. If the body control module detects a failure in a critical system or process, a limp home signal may be sent to the ECU. The limp home signal informs the ECU of a problem with the vehicle.
6) Brake lights stay on
The brake lights are controlled by the body control unit. If you have already checked the brake switch and verified that it is working, check the body control module and the brake light pin connected to it.
7) Headlights won’t turn on
The headlight circuit is usually controlled by the body control module. If both headlights stop working at the same time, check the body control module.