Symptoms Of A Bad Body Control Module And Replacement Cost

The BCM controls a wide range of systems in the car. It’s responsible for most things outside of the drivetrain.

As with every element of your car, things can go wrong. When this happens, they need fixing – don’t leave it and wait for it to get worse!

In this guide, I will walk you through the most obvious symptoms of a defective Body Control Module.

First, it’s crucial to know what the BCM does and why it goes wrong, so I will start by explaining what a BCM is.

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What Is A BCM (Body Control Module)?

The Body Control Module is one of the countless (or hundreds, in modern cars) of modules making up the ECU. The Electronic Control Unit oversees every tiny function in your vehicle.

The BCM can be (exceptionally broadly) described as the module responsible for most of the non-drivetrain functions. These include:

• Headlights, turn signals, brake lights, reverse lights, etc.
• Interior lights
• Instrument cluster lights
• Radio or infotainment system
• Power windows
• Horn
• Windshield wipers
• Heating and climate control (including air conditioning)
• Alarms and immobilizers
• etc.

The BCM takes measurements to and from these devices. It shares these with all the other modules to calculate things like alternator output.

In contrast to the BCM, the ECM (Engine Control Module) supervises the engine. The TCM (Transmission Control Module) works with the transmission. And so on.

Why Does A BCM Go Bad?

When a BCM goes defective, it’s typically down to the following:

• A glitch or error in manufacturer programming or infrastructure.
• Water or debris intrusion.
• Bad connections, wiring, or grounds.

If it’s down to a manufacturer’s fault, there may or may not be an official Service Bulletin and Recall ID.

These are more common than you might expect, but that doesn’t mean every problem is the brand’s fault. Not directly, at least.

One of the most vital parts of ECU design is ensuring there’s no way for water to get in. As an efficient conductor, water will short-circuit the modules, causing damage. This damage, in turn, prevents certain things from working.

Poor links cause a BCM to fail for identical reasons. The pathway that carries the electric energy is erratic and inefficient. This results in different currents, inconsistent measurements, and unusual outcomes. Over the years, it may result in harm.

Bad Body Control Module Symptoms

It’s challenging to pin down symptoms of a bad BCM. You could notice almost anything.

If you’d like a vague overview, watch out for any enigmatic problems with any component controlled by the BCM.

Don’t forget, these include any electrically-powered part apart from the engine- and transmission-related components. Check out that list in the initial section.

That said, here are a couple things for you to watch out for.

1. Erratic Component Behavior

Faults with the BCM will almost certainly result in peculiar behavior from the relevant components. Here are a few examples.

1. The horn goes off at random intervals.
2. Windshield wipers come on unexpectedly or move slower or quicker than usual.
3. Lights flicker on and off.
4. The instrument cluster has a close resemblance to a 1980s disco.
5. Power windows stop working or seem to be struggling.
6. The alarm sets off at random times.

What you might think of as being nothing more than a defective motor or faulty ground could be a malfunctioning BCM. Unfortunately, you might not discover this until you’ve replaced the component, only to find the issue persists.

It’s relatively typical for a customer to bring their car to a mechanic for a new light or wiper device, just to find out that they require $1,000 worth of essential ECU repairs.

2. Battery Draining Faster Than Usual

All aging batteries lose their ability to hold a charge. If you need to jump-start your car every day, it might be as simple as getting a new one.

But, the problem may be because of the BCM. The Body Control Module often leads to parasitic drain, which is a common issue.

In brief, a parasitic drain is when a component stays on when it should turn off with the vehicle.

It’s not just the BCM that causes them – any electrical circuit might – but it’s most frequently related. The module might continue to power an internal light indefinitely, for instance.

Parasitic drains can entirely drain your battery in a matter of hours. That’s extremely bad for it.

If you notice that your new battery is often depleted, take your car to a mechanic. You should get a new battery if it’s in poor condition.

While they replace it, for some comprehensive ECU diagnosis, you might need to go to an automotive electrician directly.

3. Problems Starting

When the BCM goes defective, it might affect the manufacturer’s pre-installed anti-theft system.

Any of the following (and more) could happen:

• The alarm goes off when you try to start the engine
• You don’t hear anything (not even a click) when you turn the key in the ignition

These both stem from the fact that the ECU doesn’t recognize the key’s relationship with the car. As a result, it defaults to its anti-theft setting (whatever that entails explicitly).

4. Other Access And Security Issues

Since the Body Control Module is also accountable for operating the access systems, you might observe issues here, too.

For example, the doors might lock or unlock at random intervals. Another common problem is the doors re-locking immediately after you press UNLOCK.

It’s not just keyed systems, too. Keyless entry might cease functioning or activate the alarm when you open the door.

If you notice any kind of peculiar problem, there’s an electrical issue somewhere – without a doubt. This problem might rest with the BCM.

Is It Safe To Drive If I Have A Bad BCM?

It isn’t safe to drive with a faulty Body Control Module.

This isn’t because of any impending drivetrain failure. The BCM communicates with the ECM and TCM but doesn’t influence them much.

Instead, you might find that specific lights suddenly stop working. Without brake lights, someone behind you could crash into you. An accident is likely if your headlights turn off as you drive through fog or darkness. Windshield wipers might not work in the rain, and so forth.

For this reason, it’s optimal to have your car towed to an automotive electrician if you have cause to suspect a faulty BCM.

Bad Body Control Module Repair & Replacement Cost

There are three potential ways your faulty BCM might be repaired. In order of costliness, these are:

1. Control Module reset
2. BCM reprogramming
3. BCM replacement and reprogramming

Control Module Reset

If there’s nothing more than a defect in the BCM, a reset might fix it. Each manufacturer designs a “reset” option into its operating systems.

It’s crucial to follow the official recommended advice here. If you don’t, you might inadvertently do some much more serious damage.

In most cases, it involves disconnecting the battery or removing a fuse for a particular length of time.

It’s best to leave it to the mechanic. They will do it thoroughly and safely.

In this case, you should only have to pay a diagnostic fee. In sum, it should be less than $100.

BCM Reprogramming

In most cases, you don’t need a brand-new module unless it’s been physically damaged.

If resetting the vehicle didn’t work, you might need to get the BCM reconfigured.

To do this, an automotive electrician connects to your car and checks for flaws. These need to be fixed, and the source of the problem also needs to be found and adjusted.

You only have to pay for the work done, which involves adept workers. The final cost may range from $300 to $600 or possibly higher, depending on the extent of the issue.

BCM Replacement and Reprogramming

If the BCM has been physically harmed (by any number of things), you need a new unit.

The following may cause harm to the unit:

• Being in an accident
• Water intrusion
• Dust/dirt/debris getting in
• Overheating
• Inadequate protection against humid air
• Poor protection against electrical transients (bursts of energy)
• Bad solder joints
• Components damaged during production
• Criminal tampering
• and much more.

On average, a new BCM unit costs around $400 in parts. Add another $200 to $300 for labor. This includes both installation and electronic downloads.

In total, you should expect it to be roughly $600 to $700.

Conclusion

A faulty BCM module isn’t the best prognosis, and it can be challenging to spot. However, it should be a relatively straightforward fix once you’ve zeroed in on the problem.

The issue here isn’t really the subpar BCM itself – it’s what caused it. Yes, you’ve paid a substantial sum for a new one, but will the problem happen again?

That’s why it’s crucial to use automotive electricians – specialists who know their way around a car’s electrical system.

They’re your ideal bet for not just repairing but resolving your BCM problem.