What Is Powertrain Control Module (PCM)?

Modern vehicles are complex, consisting of several systems that work together to ensure their smooth performance. They rely on computers like the PCM or powertrain control module to stay on top of their functions.

What Is a Powertrain Control Module (PCM)?

A power-train control module, abbreviated PCM, is an automotive component, a control unit, used on motor vehicles. It is generally a combined controller consisting of the engine control unit (ECU) and the transmission control unit (TCU).

On some cars, such as many Chryslers, there are multiple computers: the PCM, the TCU, and the Body Control Module (BCM), for a total of three separate computers. These automotive computers are generally very reliable.

The PCM commonly controls more than 100 factors in a car or truck. There are many hundreds of error codes that can occur, which indicates that some subsection of the car is experiencing a problem.

When one of these errors occurs, usually it will turn on the “check engine” light on the dashboard. The PCM is one of potentially several on-board computers, or essentially the “brain” of the engine control system.

The primary inputs to the PCM come from many sensors, of different types, that are spread around the car. Most of them are oriented toward engine management and performance. These sensors fail at a much higher rate than any of the computers do.

Functions of the PCM

• Engine Management: It controls various engine functions such as fuel injection, ignition timing, air-fuel ratio, and emissions controls. This ensures optimal engine performance, fuel efficiency, and compliance with emission standards.
• Transmission Control: It manages gear shifts, transmission fluid pressure, and other aspects of the transmission system to ensure smooth and efficient operation.
• Diagnostics: The PCM monitors and diagnoses faults within the powertrain system. It stores diagnostic trouble codes (DTCs) which can be read using an OBD-II scanner to help in identifying issues.
• Adaptive Learning: The PCM can adapt to changing conditions and driving habits by adjusting various parameters for improved performance and efficiency over time.

How Does the PCM Work?

The PCM receives signals from sensors that measure air flow into the engine and out the exhaust, the coolant temperature, how far down the accelerator pedals is, the speed at which each wheel is turning and other parameters.

It then uses that information to make dozens of decisions per second, such as how much fuel to inject into each cylinder, when to fire the spark plugs and when an automatic transmission should shift to a different gear to deliver the best performance for the current conditions.

Some vehicles refer to the PCM as the “engine control module” or “electronic control unit.” Others, mainly older ones, have separate control modules for the engine and automatic transmission that stay in constant contact with each other — like BFFs on their iPhones — because the transmission reacts to what the engine is doing and vice-versa.

When this flow of information between the PCM and other onboard computers and sensors works properly, the result is smooth and efficient performance, with the PCM seamlessly making necessary changes without any fuss.

But as fast and smart as PCMs can be when all is well, they can be dumb as bricks when things go wrong. For example, if an oxygen sensor in the exhaust system conks out, the PCM will be scratching its digital head and unable to figure out how to adjust the air-fuel mixture going into the engine.

The check engine light will probably go on — a cry for help — and the engine might run roughly, have sluggish acceleration or other issues. Likewise, if the PCM fails, the engine won’t start.

Because PCMs rely so heavily on inputs from other sources, they sometimes are falsely accused of causing a check engine light or engine problem.

Even if the trouble code for a check-engine light points to the PCM, mechanics test PCMs and often check inputs to make sure it is the culprit before replacing it. 

Can a Car Overheat if the PCM Fails?

Yes, a car can overheat if the PCM fails. Here’s how PCM failure can contribute to overheating:

• Incorrect Fuel Mixture: The PCM controls the air-fuel mixture in the engine. If it fails, the engine might run too lean (not enough fuel) or too rich (too much fuel), both of which can lead to increased engine temperatures.
• Cooling Fan Control: The PCM often controls the operation of the electric cooling fans. If the PCM fails, the fans may not operate when needed, leading to insufficient cooling of the radiator and engine.
• Ignition Timing: The PCM adjusts the ignition timing to optimize engine performance and prevent knocking. Improper timing can cause the engine to run hotter than normal.
• Sensor Failures: The PCM relies on data from various sensors, including the coolant temperature sensor. If the PCM fails to read this data correctly, it may not properly manage the engine cooling system, leading to overheating.
• Transmission Issues: Problems with transmission control can lead to increased engine load and heat production, especially if the transmission is not shifting correctly or is stuck in a gear.

What Causes PCM Failure?

PCMs are generally built to last longer than any of a car’s sensors. More often than not, software concerns—not internal hardware problems—cause PCM issues.

Other common causes of PCM failure include an overload from a shorted component or circuit, power surges, charging system problems, and environmental issues, such as moisture and extreme temperatures.

What Are the Symptoms of a Bad PCM?

Because the PCM is responsible for a wide range of vehicle operations, it can cause many problems when it fails. Here are some of the most common telltale signs of a bad PCM.

#1. Engine Light Illuminates.

The Check Engine light that illuminates on your dashboard is the first sign of a bad PCM. But keep in mind the Engine Check light can relate to other symptoms (a bad sensor, wiring problem, or something else).

So you need to check your vehicle with the DIY scan tool to verify that the PCM is causing your Check Engine light to turn on.

#2. Poor Performance.

The PCM is the brain behind the operation of the ignition system and the fuel system. It receives the value of the throttle position sensor and camshaft position sensor to calculate the amount of fuel needed to be delivered and the ignition timing precisely.

And a lousy PCM poorly performs this calculation. The results of this issue are the following:

• Losing power
• Rough idling
• Slow accelerating

#3. Hard Starting.

A bad PCM can also cause hard starting. because the PCM has errors in controlling the ignition and fuel system. If the PCM fault is more serious, your vehicle may not start.

#4. Increased Emissions.

When your vehicle is working correctly, the PCM minimizes the vehicle’s emissions by optimizing ít engine performance.

However, when the PCM is not working as it should, the performance suffers, and the emissions increase. However, excess emissions may not be noticeable without an emissions test.

#5. Poor Fuel Economy.

When engine control is faulty it is not surprising that fuel economy suffers as a result. For example, faulty combustion results from the PCM miscalculating and communicating incorrect values to the powertrain components. There are multiple ways a bad PCM can reduce gas mileage.

#6. Shifting Problems.

Erratic or random stuck shifting is one of the most severe PCM failure symptoms. A faulty sensor or PCM may lead to transmission damage.

Whatever the PCM issue, you must take your vehicle for service immediately. These transmission conditions can present safety concerns or even strand you.

7. You’re Receiving a PCM-Related Error Code

The last symptom on our list is the humble error code. When your PCM experiences a problem, it logs an error code, which will display on any connected code reader device.

If this is your first sign of trouble, congratulations! You found the problem before it got any worse.

We’ve written about several of these codes in the past, including the U0100 code, the P0603 code, the P0113 code, and the P0606 code. That said, our list is not exhaustive.

Most codes beginning in “P06” involve a PCM failure, and there are some others as well. Consult your code reader’s manual for specific information on any codes you’re seeing.

There are other things that could be causing these symptoms. For example, poorly-inflated tires can cause a drop in gas mileage, and hard starting can be caused by a weak battery or failing starter.

But if you’re experiencing two or more symptoms with no other obvious cause, it’s a good idea to check your PCM.

How to Test a PCM?

Before starting any job, it’s important to have the right tools for the task. Here’s what you’ll need to test a PCM:

• Flashlight
• Standard and Philips screwdriver
• OBD or OBD II code scanner (check with your car’s manufacturer on device compatibility)
• Multimeter
• A new PCM (if replacing)

Step 1: Visual Inspection.

Now, before you start doing any surgery on your car, the first thing to do is to check for rust or a disconnected wire. This isn’t the most common cause of a PCM failure, but it’s the easiest to identify.

Make sure that your PCM is connected to your battery, and that there’s no rust on the PCM itself or on the battery wiring. Reconnect any loose wires if necessary. If your PCM has experienced corrosion, you’ll have to skip to step 5 to see if it’s failed.

Step 2: Check Your Battery.

While you’re under the hood, use your multimeter to ensure that your battery has a full charge. It should read at least 12.6 volts with the engine off, or 13.7 volts with the engine running.

If it’s showing less than that, fully charge your battery and re-test. The reason this is important is that low voltage can cause certain sensors to fail, depriving your PCM of the input it needs to make correct adjustments.

Step 3: Code Scanning.

If your battery is fully charged and there’s no visible rust, your next step will be to plug an OBD or OBD II code scanner into your vehicle and see if the PCM is producing any OBD error codes.

This can be incredibly helpful in solving many mechanical and electrical problems since you can use these codes to narrow down which systems are causing the failure.

A codebook (or easy Google access) is a necessity here since you’ll need to learn what the codes mean in order to make head or tail of them.

We’ve written about several PCM-related error codes in the past, including the P0603 code, the U0100 code, the P0113 code, and the P0606 code. Obviously, this isn’t an exhaustive list, but it represents the most commonly-displayed error codes.

Step 4: Inspect Wiring and Sensors.

Hopefully, you had some success with the previous step, because this is where things can get tricky. You need to check the sensors that are connected to your PCM, as well as the wires that connect them.

If you’re seeing a PCM code – or two, or three – it can really help you narrow in on which sensors or wires are faulty.

Perform a visual inspection of these wires, as well as checking them with a multimeter. Don’t forget to check ground wires and connection points, either, since these are frequent causes of trouble.

Once you’ve replaced any failed components, reset your car’s codes, and drive for a while. Most likely, you’ll have solved the problem.

Step 5: Try a Replacement.

If all else fails, or to confirm some repairs, you may need to try running your vehicle with a replacement PCM. Ensure that the PCM is the correct version not just for your make and model, but for the same year as well.

If it turns out that your PCM was faulty, you’ll immediately notice an improvement in performance.

How Much Does It Cost to Replace a PCM?

The average cost for a Powertrain Control Module Replacement is between $1,028 and $1,098. Its price depends on various factors, like the part’s brand, condition, quantity, and your vehicle’s specifications.

An aftermarket PCM replacement can cost you anywhere from $50 to $1000 on parts alone.

As for labor, you can expect to pay around an extra $100 to $300 to have your damaged PCM professionally replaced. Of course, this is only an estimate and might vary depending on your vehicle and the rates in your area.

What to Consider When Looking for a New PCM

Shopping for a new PCM can quickly become overwhelming because of the wide variety of options on the market. To help you choose the right one for your vehicle, here are some factors to consider when you’re in the market for a PCM replacement:

Application

Always check for fitment before buying a new PCM for your vehicle. Get a replacement that’s designed specifically for your vehicle’s year, make, and model to guarantee a perfect fit and hassle-free installation.

If you’re unsure, refer to your PCM’s replacement part number. It’s usually on the PCM itself or in your manufacturer’s catalog.

Condition

PCMs are available in new and remanufactured conditions. A new PCM is built from brand new components and materials, while a remanufactured PCM is an old but still perfectly usable module that underwent a thorough upgrade process that lets it compete with new parts.

If you’re on a budget, a remanufactured PCM will help you save money without downgrading your car’s performance.

Quality

Make sure to pick a PCM that’s made of durable and made of high-quality materials. Otherwise, you might find yourself in inconvenient or dangerous situations, like your car suddenly shutting down in the middle of driving.

The best way to ensure the quality of your new PCM is to order it from a trusted brand.

Finding the perfect replacement PCM for your vehicle should be easy as long as you follow the tips listed above and look through credible product reviews.

Also, don’t forget to check your vehicle specifications or consult your trusted mechanic to double-check the specifications of your replacement PCM.

FAQs.