What are the Symptoms of a Bad PCM?

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PCM stands for Powertrain Control Module. It is the main computer that controls all of the engine and transmission functions in your vehicle. It manages functions such as fuel injection, ignition timing, and transmission shifts. Simply consider it somewhat the brains of your car’s engine that helps to keep it running properly.

A PCM that has failed will often cause the engine to run erratically. The engine may stall, or misfire and the vehicle may experience reduced power and performance. In some cases, a bad PCM may also cause the check engine light to come on. If you suspect that your PCM is failing, it is important to have it checked by a qualified mechanic or dealership as soon as possible.

In this article, we’ll discuss the symptoms of a bad PCM, as well as what you should do if you suspect your vehicle’s PCM is failing and the costs relating to replacement or reprogramming of it. 

How the PCM Works

How the PCM Works

It works by constantly monitoring different sensors throughout the engine and transmission and making adjustments as needed to ensure optimal performance. The PCM uses input from these sensors to adjust fuel delivery, ignition timing, and transmission shifts. This helps to keep the engine running smoothly and at peak efficiency.

The PCM is constantly making adjustments based on the input it receives from sensors. When one or more of these sensors fail, it can cause the PCM to make incorrect decisions which can lead to engine performance issues.

8 Symptoms of a Bad PCM

what are the symptoms of a bad pcm?

The following are eight symptoms that can indicate the PCM is failing or has failed:

1. Check Engine Light Is On

Usually, the PCM will set a diagnostic trouble code and illuminate the check engine light when it has failed. If you notice that your check engine light is on, it’s important to have your vehicle scanned for codes as soon as possible so the problem can be diagnosed and repaired.

Also Read: Check Engine Light Flashing When Accelerating

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

An easier way to tell if the PCM has failed is by reading any error codes that have been stored. If you’re receiving a code related to the PCM, you may encounter the code P0601, which indicates internal PCM failure. Other codes related to the PCM can include  U0100, P0113, P0602, P0603, P0604, P0605, and P0606. These codes all indicate that there is a problem with the PCM.

Codes related to the PCM can be read with an OBD-II scanner which can be purchased relatively cheaply online or at most auto parts stores and connecting it to the vehicle’s diagnostic port.

3. Poor Engine Performance

The vehicle may experience poor engine performance if the PCM has failed. This can manifest itself in a number of ways such as reduced power, hesitation upon acceleration, stalling, misfiring, or decreased fuel economy.

4. Shifting Becomes Problematic

It may also have difficulty controlling the transmission and can lead to hard shifts, delayed shifts, or even no shifting at all. This is more serious as it can cause further damage to the transmission if left unchecked.

5. Misfires or Backfires

In some cases, a bad PCM may cause the engine to misfire or backfire. This is often due to incorrect ignition timing as the PCM is no longer able to correctly manage the timing of the ignition system.

6. Problems Starting

When attempting to start the vehicle, you may notice that it’s taking longer than normal for the engine to turn over or that it’s not turning over at all. In some cases, you may even hear a clicking or grinding noises coming from the starter area. These are all signs that the PCM is not sending the correct signal to the starter relay.

7. Increased Emissions

During a tailpipe emissions test, you may notice that your vehicle is emitting higher levels of pollutants than normal. This is often due to a problem with the fuel delivery system as the PCM is no longer able to correctly regulate the amount of fuel being injected into the engine.

8. Dashboard Warning Lights

However, in some cases, if the PCM itself is failing, it may not be able to set a code or turn on the check engine light, or even set multiple lights and indicators on the dashboard. In this case, you’ll need to rely on other symptoms to indicate that the PCM is bad.

What to Do if You Experience PCM Failure Symptoms

If you end up confirming or encountering any of the above symptoms, it’s important to take your vehicle to a reputable mechanic or dealership as soon as possible so they can properly diagnose and fix the issue. In some cases, the PCM may need to be replaced entirely while in other cases, a software update may be all that’s needed.

PCM Replacement Cost

The cost to replace the PCM will vary depending on the make and model of your vehicle but typically, you can expect to pay between $600 and $1200 for a new unit. Keep in mind that this is just the cost of the part itself and doesn’t include labor which can add an additional $100 to $200 or more to the final bill.

Also Read: How much does it Cost to Replace a PCM

PCM Reprogramming Cost

For reprogramming, you can expect to pay between $150 and $300 depending on the make and model of your vehicle. This is generally a quicker and cheaper fix than replacing the PCM entirely but in some cases, it may not be possible if the unit is too damaged.


So, there you have it. These are just some of the symptoms of a bad PCM and what you can expect to pay if you need to have it replaced or reprogrammed. Remember, if you’re experiencing any of these issues, be sure to take your vehicle to a reputable mechanic or dealership as soon as possible so they can properly diagnose and fix the issue.

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