Today’s vehicles depend on complex communication networks that use terminals, wires, and sensors feeding information into electronic modules that control essential vehicle systems.
One type of communication module is the body control module (BCM), which is basically the brain behind all the comfort and safety features.
While it’s uncommon, a vehicle’s body control module can malfunction severely enough to stop working altogether. Here are the most typical symptoms of a faulty BCM, as well as the cost associated with replacing one.
What is a Body Control Module?
A body control module is an electronic driver that is responsible for monitoring and controlling several vehicle body functions.
The exact number of functions a vehicle body control module monitors and controls will vary depending on the vehicle in question, but in most instances a BCM controls electronic functions such as wiper, lighting, heating, air conditioning, and anti-theft system functions.
A body control module also communicates with other control modules on the vehicle. This allows the BCM to facilitate greater integration of the major systems in the vehicle to enhance overall vehicle effectiveness and operation.
Where is the Body Control Module Located?
In the majority of vehicles, the body control module will be located beneath the dashboard. This tends to be a dependable location as most BCMs of this type will be closely!
However, a BCM may be located on either side of the dashboard (driver vs passenger) depending on the vehicle model.
In some cases, you may need to remove a portion of the dashboard and or any associated trim pieces to attain a BCM. Fortunately, almost all accessory dash items are attached together with little more than push-style clips, so this task is not usually daunting!
Signs of a Bad Body Control Module
There are many signs surrounding a body control module malfunction. Some signs of this failure seem to happen more often than others, but it is vital to learn them all, in case you need to contend with a failure like this in the future.
The following are a few of the more prevalent signs relating to body control module failure.
#1. Repeated Battery Drain.
One of the most common signs of body control module failure is repeated battery drain, or excessive draining/parasitic draw.
Following a certain amount of parasitic draw is acceptable, but excessive draining when allowed by BCM failure can drain a battery in hours, if not minutes. This draining happens due to a BCM continuing to provide power to a specific accessory at incorrect times.
#2. Erratic Electrical Operation.
Another sign of a faulty body control module is random or intermittent operation of any other vehicle electrical functions such as the horn, lights, power windows and mirrors, and wipers.
Usually, you can count on variations in operation from the instrument cluster dials rapidly sweeping from one extreme to another. Random operation of the vehicle door locks and radio is also a possible sign of body control module failure.
The odds of these problems being due to BCM failure increase dramatically when multiple symptoms as described are experienced simultaneously.
#3. Security System Problems.
In almost every security system instance, the body control module manages it. So it is pretty safe to assume, repeated weird behavior from a vehicle’s security system is due to a malfunctioning/faulty body control module.
This should also include any problems concerning keyless entry or passive entry functions on the vehicle.
#4. No Dash Warning Lights.
A faulty body control module can cause your instrument cluster to go bonkers. All of a sudden, your entire dashboard is lit up brightly, almost looking like a Christmas tree.
This occurs when the BCM is not able to communicate with one or more of the vehicle’s other control modules. The common modules attached to the BCM are the transmission control module, powertrain control module, and airbag control module, just to name a few.
#5. The car won’t start.
A faulty body control module (or, in some cases, ignition control module) can prevent a vehicle from starting at all, in certain situations.
Although this is rare, a BCM could fail to read the key’s transponder chip or fail to provide the ignition switch to the “crank” signal, thus preventing starter activation altogether.
There is a chance that, depending on how many additional control modules the BCM is “first” communicating with for “crank” activation, a communication failure from the BCM is possible, and lead to starting problems.
Can You Drive With a Bad BCM?
It is possible to drive a vehicle with a bad body control module, but that’s not a good idea, because you never know how a computer module that is in the process of failing will behave.
You can’t predict which functions of the faulty computer will work properly, if any. The issue here is that we cannot ascertain if a safety-sensitive issue may occur because of BCM failure.
Even if one hasn’t occurred in the past, one cannot say that the faulty BCM will operate the vehicle’s lighting when expected to do so, which is a calculated risk for the vehicle’s occupants.
Body Control Module Replacement Cost
The body control module replacement cost will differ from one vehicle make and model to another, because costs associated with body control modules differ, as do labor rates associated with their replacement. However, the following is an example of the typical cost for a BCM replacement.
Typically, the average cost to replace a body control module will be in the range of $300-$600. The most significant variable here is the cost of the failed module itself.
Currently, shipping costs associated with locating and getting such modules can also affect the total costs of these repairs, as module availability has become an issue.
What Causes BCM Failure?
Heat and Fatigue
Your vehicle’s body control module can be damaged by heat and high temperatures. As your engine runs, it will produce heat that can affect the electronic components of the BCM.
When a BCM gets hot enough and long enough, fatigue will happen, and it will stop working.
Water and Liquid Damage
In some instances, your BCM can be exposed to water and liquid. While a BCM has adequate protection from water damage, a severe leak or exposure to liquid can corrode or cause a short circuit to the connections, leading to failure due to water damage.
Shock and Impacts
A vehicle collision, or impacts from another vehicle, may cause significant impacts or shocks to the BCM.
While the BCM is in a fairly protected location, collisions produce significant shock loads that may be damaging the circuits, wiring, or electronic components of the module, eventually causing it to fail.
Short Circuits and Damaged Wiring
The BCM relies on numerous peripheral wires and electrical circuits to function properly. Damage to the wiring or short circuits can create BCM malfunctions that may also sometimes cause significant damage to the BCM.
As with anything on your vehicle, it is wise to address wiring issues (easier said than done), as using damaged wiring is just putting undue stress on the BCM.
Overused and Worn-Out Relays
Your body control module also relies on numerous relays to operate in an efficient fashion, such as your headlights or intermittent wipers. Over time, these relays can become overused and worn out, causing the BCM to require higher levels of effort and leading to failure on the part of the BCM.
You may want to consider, every once in a while, checking relays controlling body control module functions and replacing relays that are worn or are particularly worn out.
How a Bad BCM Affects Other Modules
Powertrain Control Module
A bad body control module can disrupt communication with the powertrain control module (PCM), your vehicle’s main computer.
Disruption in the communication between the BCM and the PCM can lead to several serious issues, such as reduced engine performance or stalling, and in some cases, a no-start condition, where typically the vehicle will turn over but not start
A faulty BCM can create warning lights, and when you’re talking about making “full” use of the efficiency of the systems the PCM controls, the communication is important.
Airbag Control Module
A bad BCM can also affect your airbag control module and potentially your safety.
When the airbag module isn’t communicating correctly with the BCM, it could create airbag warning lights to turn on or, worse, not deploy airbags in a collision. A warning light pertaining to airbag issues is important to get checked and dealt with.
Transmission Control Module
The transmission control module (TCM) controls your vehicle’s transmission, allowing your vehicle’s transmission to work properly, smoothly shift, and allowing for the performance of the vehicle. When the BCM is having trouble, this can affect the ability of the TCM to operate properly.
Further, a bad BCM can cause transmission problems such as shifting problems, decreased fuel efficiency, and poor performance of the vehicle.
Essentially, and faulty BCM can cause a sort of domino effect, leading to multiple failures in modules and/or systems in your vehicle. Even if you or your mechanic can suggest a bad BCM, you want to take that seriously before further problems arise.
FAQs.
Does a new body control module need to be programmed?
Yes, when you get a new BCM, almost certainly, the BCM needs to be programmed to match your vehicle’s settings during the install, otherwise it will not control all the myriad electronic systems and functions in your car.
You will almost certainly need professional assistance from a mechanic or dealer, as you typically need specialized tools or software in order to program any BCM.
Can a BCM be reset?
There are certain scenarios in which your vehicle’s BCM can be reset, but this depends upon the internal circuitry of the module being functional, as no reset will resolve the failure of internal electrical circuits.
If a “glitch” has occurred, causing your vehicle’s BCM issues, resetting the BCM could be exactly what is needed. The method of performing a reset of a body control module will vary from one make or model of vehicle to the next.
Ford, Dodge, and Chevy/GMC all have their own process to complete this function, but most involve interrupting the power of a vehicle’s BCM for a defined period of time.
For many, you can do this simply by disconnecting a vehicle’s battery, or another method may involve removing a fuse from the vehicle’s BCM.
Regardless of how you perform a BCM reset, you should always consult the factory-specific service publication to properly reset your car, truck, or SUV’s body control module. Inattention or carelessness can cause irreversible damage to the unit.