Top 7 Symptoms of a Bad Body Control Module

Geoff Cudd

If you are driving a modern car, there are chances that it has different control units and modules. From safety, comfort, and overall car management, these modules play their roles in the connection and control of certain parts and functions of your car.

Because there are a lot of modules in your car and failure to any of them will affect certain functions in your car, how can you figure out which module is bad? How do you know if your body control module is bad?

The body control module is the main powerhouse of your car’s body function. This includes coordination and control of electronic control units (ECUs), load drivers, and communication with your car's other security and comfort subsystems.

Some of the major symptoms of a bad body control module include communication failure, poor performance of driving and comfort modules, failure in door lock functions, and other safety and security systems.

Let’s learn more about these symptoms and answer other bad body control module-related questions.

Bad Body Control Module Symptoms Video

Common Symptoms of a Bad Body Control Module

The symptoms of a bad body control module depend on the fault and damage to the module. Shorting wires or an internal electrical problem might present a symptom different from damaged sensors.

These bad body control module symptoms will range from operational issues to the total breakdown of some features in your car.

Here are 7 common symptoms of a bad body control module.

1. Problems in Other Modules

Your Body control module controls and monitors the operations of other modules in your car. When they go bad, you should expect a malfunction of other modules.

You should expect erratic behaviors from your alarm system, lights, wipers, or comfort and security elements. This is because the BCM receives and monitors signals from all modules in your car, except those connected to engine performance.

You can tell that your body control module is bad if you notice some unusual activation and deactivation of your modules.

2. Triggers Check Engine Light and Other Dash Warning Lights

Suddenly, you notice that your dashboard looks like a Christmas tree. Many warning lights are triggered without justifiable cause. This usually happens because you have a bad body control module.

The body control module receives signals and communicates with other modules in your vehicle. This includes interaction with the anti-lock brake module, driver assistance systems, power windows, power train control module, airbag control modules, and lots more. When it goes bad, communication fails.

This generates an information cluster that can trigger error codes or warning lights across all connected systems. This will result in multiple warning lights because the BCM fails to interpret sensor signals.

3. Electrical Malfunction

It would be best if you understood that the body control module plays a crucial role in the performance of your electrical systems.

Your interior and exterior lights, wipers, power windows, headlights, door locks, parking sensors, power mirrors, central locking, air conditioning immobilizer system, etc.

These electrical malfunctions caused by a bad body control module can manifest in auxiliary units.

If you notice that your basic electrical systems are starting to misbehave, you should check your BCM.

4. Communication Failure

One of the symptoms of a bad body control module is the lack of communication across modules and auxiliary components in your car.

A bad body control module will cause communication failure between the integrated control units of your car through your vehicle bus system (CAN, LIN, or ethernet).  The communication failure can extend to the lack of identification in your car, poor transmission, and faulty computer functions.

The failure is not limited to a few sets of systems. Many units are affected by the bad control module. The effect can go as far as causing your car not to drive.

5. Failure in Driver Assist Systems

Most car manufacturers integrate BCMs to provide targeted software solutions that improve drivers’ experience. This can include integrating smart car data, predictive maintenance, and other driver assistance systems.

BCM functions extend to advanced driver assistance and authorization systems. You can tell your BCM is bad if your driver assists systems start performing poorly.

6. Poor Performance of Safety and Security Systems

The overall safety, security, and comfort of your car and the passengers are monitored and controlled by your BCM. This includes your seat control, anti-theft, and remote keyless entry systems.

The body control module contains your door lock functions, vehicle anti-theft security system (VTSS), passive anti-theft system (PATS), etc.

This includes your high beam headlamps, horns, chime warning, gauges, speedometer, odometer, and fog lamps. If your body control module goes bad, your car’s security and safety systems will malfunction or stop operating.

7. Battery Drain

Brain drain, also known as the parasitic drain, is one of the most typical symptoms of a bad body control module. When your body control module is bad, most car systems will continue running even after turning off your car.

When your car is off, the continual power supply to these systems will cause huge battery drainage. Did you park your car overnight to wake up to a dead battery? There are chances that you have a bad body control module.

Can a Bad BCM Cause a Car Not To Start?

BCM does not affect the performance of your car’s engine but can cause your car not to start. Your BCM controls and monitors the operation of your car’s remote keyless entry system. If the BCM is bad, there are chances that your remote keyless entry system won’t work, and your car won’t stay.

This also happens when your BCM fails to identify your key’s transponder chip. The BCM can also fail to interpret and deliver a start signal to your car’s ignition system. The bridge in communication from a bad BCM can cause a car not to start.

What Does a Body Control Module Do?

The body control module regulates and monitors the performance of electric components in your car. This extends to the smooth operation of security and safety systems, AC systems, lighting, and features that ensure drivers’ comfort.

The body control module acts as a collection point for other modules, helping them interconnect from a single source while performing separately.

The role of a body control module differs according to its design and type. There are BCMs for inputs, outputs, and overall computer tasks. This includes collecting and interpreting sensor data from position sensors, temperature sensors, speed, etc.

The output function regulates signals for seat operations, wiper, interior, and exterior lighting, HVAC, doors, sunroof, LIN/CAN Flexray, and other electrical components in the car. This includes both analog and digital signals.

The body control module also oversees the performance of your car’s security and safety systems and predictive maintenance data capture, as seen in the anti-theft alarm, mileage calculation, CO2 output, and diagnostic reports.

What Causes a Body Control Module To Go Bad?

Here are some factors that can cause a body control module to go bad.

• Wear and tears
• Corrosion from excess engine heat
• Voltage overload
• Shorting of wires or falling internal connection
• Hard impact collisions and vibrations
• Damaged sensors
• Water and liquid splashes

Can a BCM Be Reset?

Yes.  A BCM can be reset and reprogrammed. It would be best if you didn’t use a “used” BCM without resetting or reprogramming it. A car dealer or specialized mechanic can help you reset your BCM.

The procedure for resetting a BCM might vary for different cars, but it usually centers on cutting off the power supply or disconnecting the fuse. BCM reset cost ranges from $150 - $300. The cost might go as high as $800.

We wouldn’t advise that you reset your BCM if you have no experience with doing so. A proper diagnosis from an expert will determine if a BCM reset is necessary.

Can You Unplug the BCM?

Yes, you can unplug and replug the BCM. The problem doesn’t lie in safely unplugging your BCM, but if you will need to reprogram it after unplugging it.

The truth is, you can unplug your BCM without resetting or reprogramming the module. This is as long as you unhooked the battery before doing so.

Most BCMs function with EEPROM’s data systems. This eliminates data volatility, making it non-dependent on continuous power to store data.

Does a Used BCM Need To Be Reprogrammed?

Yes. Used BCM needs to be reprogrammed. You need to reprogram and flash them to allow them to link/sync properly with the sensors and units of the new vehicle.

Without reprogramming the used BCM, there is a high chance it won’t function properly.

How Long Does It Take To Replace A Body Control Module?

There is no specific time attached to replacing a body control module. It usually takes close to an hour to replace a body control module.

This depends on many factors like whether the mechanic will have to reset the BCM or not and the make or model of your car.

Summary

A bad body control module can present tricky symptoms that may make it difficult to pass a firm decision if they are bad or if the individual component is bad.

If you notice any of the bad body control module symptoms we’ve mentioned, swiftly hire the services of a professional mechanic for inspection and repair.