6 Symptoms of a Bad PCM (and Replacement Cost)

Last Updated on July 24, 2020

The Powertrain Control Module (PCM) is a sophisticated piece of machinery. It receives data from a range of sensors. The Engine Control Module (ECM) and the Transmission Control Module (TCM) are both examples of systems that the PCM monitors.

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Remarkably, the PCM also analyzes the data it collects. It uses that information to control the ignition system, the fuel injectors, and more. It will work out the best settings for optimal performance and adapt accordingly.

If your vehicle has a bad PCM, you can expect to have some serious issues. Below are some common symptoms to help diagnose a faulty powertrain control module as well as the average cost to replace and/or reprogram the PCM.

How the PCM Works

It doesn’t matter if you own a Ford or a Chevy, the PCM relay will be similar. It is the car’s brain, and it controls everything in the vehicle.

A bad car computer is a big deal. Problems with this system mean that it can’t send messages to other systems within the vehicle. It could mean throwing your timing and other vital systems out, too.

Top 6 Bad PCM Symptoms

The best way to diagnose an issue with this system is to go to a qualified auto-electrician. They have specialized equipment that allows them to read the error codes that the PCM is emitting. In the meantime, here are six classic symptoms to diagnose a PCM problem.

#1 – Poor Performance

When you’re tired, you don’t operate at peak efficiency. If you’re fatigued or ill, you have a kind of brain fog that makes it harder to think. It’s easy to make the wrong decisions and make mistakes.

Your PCM might not be at risk of the flu, but when it’s “sick,” the mechanism is going to make errors. It could misinterpret the air/fuel mix, for example, and not send the engine the necessary amount of fuel.

If there’s too little fuel, the engine won’t function properly. It will start to jerk and possibly even stall. If this continues over an extended period, the engine could become permanently damaged since it is not getting the lubrication it needs.

If there’s too much fuel, though, the engine won’t be damaged straight away. What you will notice is an increase in emissions and a decrease in fuel economy. If this is not corrected quickly, it will emit too much carbon and adversely affect the engine’s performance as well.

#2 – Shifting Becomes Problematic

incorrect transmission shifting

If the car starts shifting unnecessarily, it’s a reasonable indication that something is wrong with your PCM or TCM. But it could also indicate problems with the transmission valve body or simply being low on transmission fluid.

#3 – Misfires or Backfires

cylinder misfire causes

If the engine misfires a lot or backfires, it can mean a variety of issues so it’s best to take your car to the mechanic. They can then analyze the error codes and tell you the nature of the problem.

While causes of engine misfires are usually ignition related or a problem with fuel delivery, it’s possible a faulty PCM is to blame.

#4 – Problems Starting

bad ignition switch symptoms

For the engine to run as it should, the PCM ensures that everything is in the correct position. It also coordinates the timing of the ignition. If the timing is off, the spark plugs won’t ignite at the right times.

It leads to problems running the car. If this is the issue, the vehicle may crank over, but it won’t start.

#5 – Increased Emissions

The downside of burning more fuel is that your emissions increase. If there is too much fuel, the catalytic converter won’t be able to filter out all the harmful fumes. You will experience higher emissions, and you might even fail an emission test, so you must have it sorted out.

Related:  Best Catalytic Converter Cleaners to Help Pass an Emissions Test

#6 – Dashboard Warning Lights

If more than one warning light comes on, it is a sure indication of trouble on the horizon. The car is not operating optimally, and there are bound to be problems between the different systems.

If your dashboard lights up like a Christmas tree, get to an auto mechanic that specializes in electrical work as soon as possible.

PCM Replacement Cost

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PCM replacement cost

The PCM is such a critical system that you’d expect the parts to be costly. You’d be right. Because some powertrain control modules are much more complex than others, prices can vary a lot from one vehicle to another.

For instance, the owner of a new Audi A8 will be paying much more for a new PCM versus someone who owns a 15-year old Ford Focus.

The labor charges are also higher than they would be with your typical mechanic, so factor in an hourly rate of around $120. Fortunately, installing a new system is relatively simple so that labor won’t be too much of a factor.

You’re looking at $500 to $1,500 for a new module and another $120 at minimum for the labor. If you go to a dealer, expect to hand over a lot more cash, but, in this instance, it’s not essential to visit one. If you choose a reputable auto-electrician instead, you can save a lot on the replacement cost.

Sometimes you may be able to purchased a used powertrain control module for a couple hundred dollars whether online or from a junk yard but keep in mind that reprogramming it will be necessary. So you need to factor in the additional costs as well.

If the car still runs, you can drive it to the mechanic to save yourself the towing fees. Get it sorted out as quickly as possible, though, before some of the critical systems suffer damage. 

PCM Reprogramming Cost

powertrain control module reprogram cost

Do Windows updates drive you crazy? If so, we have some bad news for you. Your car’s computer may require an update to run efficiently.

The PCM uses software to control the systems in the vehicle. It knows that when you’re driving up a steep incline, you need more power, for example.

The programmers will think of every possible problem and program in a solution. Except that, much like with Window’s programmers, they can make mistakes, or they might miss a particular issue.

Downloading the updates is an essential part of keeping your car running optimally. Most often, a manufacturer will issue an update or recall and let the vehicle’s registered owner know a software update is necessary.

These types of updates are almost always free of charge. You will simply have to take your car to the dealership and set aside some time for them to make the updates.

But if you purchased a used PCM as a replacement (usually from a vehicle that was totaled in an accident), you will need to have it reprogrammed for it to be able to work with your vehicle.

How much it costs depends on where you’re going for the updates. There are no parts involved, so you’re looking at a standard labor charge. Prices could range from $80 to $150, depending on the service location you choose.

The process takes around about half an hour, but keep in mind that most auto-electricians charge you for at least one hour of work. PCM reprogramming is also one of the few times we’ll recommend a dealership over an independent mechanic.


10 thoughts on “6 Symptoms of a Bad PCM (and Replacement Cost)”

  1. I need a pcm for a 1993 ford mustang lx flashed. Can’t find anyone in East Texas that can do it . anybody know of anyone that can help in my area???

  2. My car was working fine then the next day CEL flashes on start up. I get codes for high voltage and low voltage on the same components. Is it a PCM or an actual misfire and emissions issue?

  3. My engine recently seized on me and during diagnostic tests everything cleared as ok and it was determined it was the engine failing. After putting in the engine, they say the PCM is out and I have to cover expense on replacement…how does the PCM work before the engine fails and then fail after engine replacement?

    • What diagnostic tests were performed? It sounds like they misdiagnosed your vehicle, thought it was the engine, then realized it was the PCM after all. I’m not sure.

  4. Too bad the PCM doesnt diagnose itself prior to expensive unnecessary repair bills. Or is it like “One of the quack doctors turned out to be a patient” and it wont tell you what it cant know?

    • It’s a little like that, yes. However I think many people misdiagnose an electrical issue as a fault with the PCM pretty regularly. It’s often a lot easier to replace a module than to hunt down a short or a bad ground.


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