Top 7 Symptoms of a Bad Body Control Module

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Geoff Cudd

Geoff Cudd

I am a serial entrepreneur and a consumer advocate. When I’m not helping car buyers, I love working on ventures that have a positive impact.

I run a cause marketing agency and serve on the board of Vayu Global Health where we are disrupting the medical industry and preventing the needless deaths of mothers and babies during childbirth.

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We get it—keeping up with the technological heartbeat of your modern vehicle feels daunting, especially when it comes to the Body Control Module (BCM). This unsung hero quietly ensures your drives are safe, your rides comfortable, and your car’s security tight.

Think of the BCM as the conductor of an orchestra, where every note must be perfect, from the flick of the turn signal to the click of the lock. But when something's off, like your dashboard lighting up unexpectedly or your car's battery draining fast, it's a sign that your BCM might need a closer look.

Here, we're not just talking tech; we're sharing a roadmap to navigate those moments, ensuring you can spot the early signs of trouble and act swiftly. Because at the end of the day, we're all in this journey together—making sure your car stays reliable, mile after mile.

Let's demystify the BCM, making sure you're equipped to keep your vehicle at its best.

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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

• Check for Error Codes: Use an OBD-II scanner to check for error codes that might indicate which module is experiencing issues due to the BCM malfunction.
• Module-specific Diagnostics: Perform module-specific diagnostics using a multimeter to check for proper voltage and ground connections, especially for systems showing erratic behavior.
• Visual Inspection: Check for any visible signs of damage or loose connections in the wiring that connects the BCM to 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

• Diagnostic Scan: Conduct a comprehensive vehicle diagnostic scan to identify specific codes related to BCM or the systems it controls.
• Circuit Testing: Test the circuits related to the warning lights for any short circuits or ground issues that could trigger the lights erroneously.
• BCM Inspection: Inspect the BCM for signs of physical damage or corrosion that could affect its functionality.

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

• Electrical System Check: Use a multimeter to test the electrical outputs from the BCM to various systems (e.g., lights, wipers) for any irregularities.
• Fuse and Relay Inspection: Check all fuses and relays associated with malfunctioning systems for damage or failure.
• Wiring Inspection: Examine the wiring harness from the BCM to different components for any wear, tear, or disconnections.

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

• Bus System Check: Test the vehicle's bus system (CAN, LIN, Ethernet) for continuity and proper signal transmission.
• BCM to ECU Communication: Verify communication integrity between the BCM and other critical control units like the ECU with specialized diagnostic tools.
• Reset/Reboot: Sometimes, resetting or rebooting the BCM can restore communication. This should be done with caution and potentially by a professional.

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

• System-specific Diagnostics: Run diagnostics on each affected driver assist system to pinpoint communication breakdowns from the BCM.
• Software Update Check: Ensure all systems, especially those integrated with the BCM, are updated to the latest firmware or software versions.
• Sensor Calibration: Check and recalibrate sensors related to driver assist systems, as misalignment can indicate or cause BCM issues.

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

• Security System Test: Manually test each safety and security feature (e.g., door locks, alarms) for functionality.
• BCM Configuration: Verify that the BCM configuration settings are correct, as incorrect settings can impact system performance.
• Component Testing: Test individual components of the security system, like sensors and actuaries, for failure or malfunctions.

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

• Parasitic Drain Test: Perform a parasitic drain test to identify if the BCM or connected systems are drawing power when the vehicle is off.
• BCM Sleep Mode: Check if the BCM properly enters sleep mode after the vehicle is turned off; continuous operation can lead to battery drain.
• Battery and Charging System Test: Ensure that the battery and charging system are functioning correctly to rule out other causes of 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.

Preventative Care and Early Detection for BCMs

Maintaining the Body Control Module (BCM) in your vehicle is crucial for ensuring the reliable operation of various electrical and electronic components. Here are some strategies for preventative care and early detection of potential BCM issues:

Regular Vehicle Diagnostics

• Scheduled Checks: Incorporate BCM diagnostics into your regular vehicle maintenance schedule. Use an OBD-II scanner to monitor for any early warning signs or codes that may indicate a problem with the BCM or related systems.
• Software Updates: Ensure that your vehicle's firmware and software are up to date. Manufacturers may release updates that improve BCM functionality or fix known issues.

Visual Inspections

• Wiring and Connections: Periodically inspect the wiring and connections leading to and from the BCM for signs of wear, corrosion, or damage. Addressing these issues early can prevent future malfunctions.
• Physical Inspection: Check the BCM itself for any signs of physical damage or corrosion, especially if your vehicle has been exposed to water or high humidity environments.

Environmental Considerations

• Moisture and Corrosion Prevention: Keep the vehicle's interior, especially the area around the BCM, dry and free from moisture. Use silica packets or other moisture absorbers if necessary.
• Temperature Control: Avoid exposing your vehicle to extreme temperatures for prolonged periods, as this can affect electronic components' functionality, including the BCM.

Electrical System Care

• Battery Maintenance: Regularly check the vehicle's battery health and ensure it's operating within normal parameters. A failing battery can cause voltage fluctuations that may impact the BCM.
• Surge Protection: Be mindful of jump-starting procedures and ensure proper connections to avoid electrical surges that could damage the BCM.

Early Detection Tips

• Monitor Vehicle Behavior: Pay attention to any unusual behavior in your vehicle's electronic systems, such as erratic lights, malfunctioning accessory controls, or unexplained battery drain. These can be early indicators of a BCM problem.
• Prompt Diagnosis and Repair: If you suspect a BCM issue, seek a professional diagnostic to identify and address the problem promptly. Early intervention can prevent more significant issues down the line.

Differentiating Between BCM Issues and Other Vehicle Problems

Vehicles today rely heavily on electronic systems, making it challenging to pinpoint the root cause of issues when they arise. Symptoms associated with a faulty Body Control Module (BCM) can sometimes mirror those of other vehicle problems. Understanding how to differentiate between BCM issues and other common vehicle issues is essential for accurate diagnosis and repair.

BCM Issues vs. Alternator Problems

• Symptoms Overlap: Both BCM issues and alternator problems can lead to electrical malfunctions, such as flickering lights or dead batteries.
• Differentiation: Alternator problems often present with a whining noise, battery warning light on the dashboard, and dimming lights that worsen with vehicle operation (e.g., when using the AC). BCM issues, however, do not typically cause noise and are more likely to result in erratic electrical behavior unrelated to engine load.

BCM Issues vs. Faulty Ignition Switch

• Symptoms Overlap: Difficulty starting the vehicle can be a symptom of both a bad BCM and a faulty ignition switch.
• Differentiation: A faulty ignition switch may cause the key to turn freely without starting the engine or electrical accessories to malfunction when the key is at certain positions. BCM-related start issues are more likely to be accompanied by security system malfunctions, such as problems with the remote keyless entry.

BCM Issues vs. Dead Battery

• Symptoms Overlap: A vehicle that won't start could be due to either a dead battery or a BCM issue that prevents the car from starting.
• Differentiation: A dead battery is usually indicated by a slow engine crank or the inability to crank the engine at all, often after leaving lights on or similar drain. BCM problems might still allow the engine to crank but prevent the car from starting due to security system miscommunication or failure to recognize the key's transponder chip.

BCM Issues vs. Faulty ECU (Engine Control Unit)

• Symptoms Overlap: Both a faulty BCM and ECU can lead to dashboard warning lights, engine performance issues, and erratic behavior of vehicle systems.
• Differentiation: ECU problems typically impact engine performance directly, such as misfires, stalling, or poor fuel economy. BCM issues are more likely to affect non-engine related systems, like interior lighting, power windows, and security systems.

Diagnostic Steps

• Use of Diagnostic Tools: Utilizing an OBD-II scanner can help differentiate between these issues. Error codes specific to the BCM or other components can guide the diagnosis.
• Professional Inspection: Due to the complexity of modern vehicle electronic systems, consulting with a professional mechanic for a thorough inspection is often the most efficient way to accurately diagnose and differentiate between these problems.

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?

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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.