Can a Bad BCM Cause a Car Not to Start?

Since the 1990s, modern vehicles have been equipped with modules to control the operation of most of their electrical components. A typical vehicle would have 10 or more modules that communicate over data lines or hard wiring.

This diminished the need for extensive wiring between components, saving manufacturers from the added weight and cost. It also made it easier to install parts at the factory and made servicing them later less complicated. One of the modules that play an important role in vehicle operation is the body control module.

Can a Malfunctioning BCM Keep Your Vehicle from Starting?

The short answer is yes, on some vehicles. A body control module (BCM) that isn’t properly receiving or transmitting signals can prevent certain vehicles from starting, depending on the system design.

The BCM is responsible for managing various electronic systems like the keyless entry and passive anti-theft (chipped key), the ignition switch, and the security system. Again, a bad BCM can cause a car not to start in some cases. 

If the BCM fails to communicate with these systems or sends incorrect signals, it can prevent the car from starting. For example, if the BCM does not recognize your key’s transponder chip or does not send a start signal to the ignition system, the car won’t start.

Here’s how it works on a 2007 Silverado. Circuit Description (Key Start):

When the ignition switch is turned to the START position, a discrete 12-volt signal is supplied to the Body Control Module (BCM) notifying it that the ignition is in the Start position. The BCM then sends a message to the Engine Control Module (ECM) notifying it that CRANK has been requested. 

The ECM verifies that the transmission is in Park or Neutral. If it is, the ECM then supplies 12 volts to the control circuit of the crank relay. When this occurs, battery positive voltage is supplied through the switch side of the crank relay to the S terminal of the starter solenoid.

One of the trouble codes triggered by a BCM problem is the U0140 code. To understand why, let’s take a closer look at how this device works and how it affects vehicle operation.

What Is a Body Control Module (BCM)?

The BCM often acts as  a gateway module responsible for monitoring and controlling all other sub-computers in your car. It is in charge of managing all your automotive electronic systems such as security systems, electric locks, car lights, power mirrors, and air conditioning systems.

Each BCM is manufactured differently and has functions exclusive to specific car makes and models. Some BCMs focus only on overseeing the car’s electrical accessories (e.g., the power locks and windows) while others, together with other ECUs (Electronic Control Units), play a role in more advanced systems, such as the immobilizer.

Where Is the BCM Located?

The body control module location can differ from one car to another but it’s always under the instrument panel. The problem is there are a lot of modules of various sizes and so you can’t just find it randomly without doing research on your particular vehicle (make, model, and year).  In case you’re unsure where your BCM is, check your vehicle’s manual or you may ask a professional mechanic to point it out to you.

What Causes a BCM to Malfunction?

Hard impact collisions, loose wiring harnesses, shorting of wires, excessive heat from the engine, and damaged sensors may interfere with the operation of the BCM.

Keep in mind that a no-start condition may be triggered by issues in different parts/systems, and not just the BCM. Therefore, it’s best to consult a qualified mechanic to get a proper diagnosis and avoid unnecessary work on your vehicle.

Order a Replacement Body Control Module From the Comfort of Your Home

If your car has a problematic BCM, it’s best not to drive it until the BCM is replaced. Control module-related issues can get costly to repair, so you want to avoid aggravating the existing problem. Fortunately, you can get a quality BCM from CarParts.com–and you don’t even have to leave your home for it.

CarParts.com provides you with straightforward and secure online shopping for replacement BCMs. Simply enter your vehicle’s year, make, model, and engine into our vehicle selector to see a list of compatible parts. Ordering takes just a few clicks or taps, and you can ask our customer service team for assistance. Our parts are ready to ship from our nearby distribution centers, so your new part will arrive in a few days.

Choose from CarParts.com’s wide selection of body control modules for various makes and models. Don’t miss the best deals on a new BCM and order today!