Six Signs of a Bad PCM and Replacement Cost

You may not like the fact that your car is filled with computers. Although these computers may seem like a wonderful thing when they work as they should, it can quickly turn to a nightmare if the circuits stop working.

This is a good thing for everybody because computers fail very rarely. Because when they do, they’re expensive to replace. Powertrain Control module is one such computer. This module controls every aspect of the powertrain.

In this comprehensive guide, we’ll break down everything you need to know about your PCM and what you need to do if it starts acting up. Let’s start with a look at the signs to look for:

Bad Powertrain Control module (PCM) symptoms

Poor engine performance and a check engine lamp on the dashboard are two of the most obvious signs that a PCM has failed. There may also be transmission problems such as shifting issues. Emissions and fuel consumption are also common.

While it’s not common for a PCM to break, it does happen from time to time. It is important to first rule out possible reasons before you go straight for the PCM.

Below is a list with more details of six symptoms that indicate a PCM problem.

1. An engine check light

A check engine light is the first indication that your PCM may be having problems. This could indicate a problem with the engine or powertrain. Keep in mind, however, that it could be a problem with wiring or the sensor.

Check for any other reasons your vehicle may have before you call the PCM. An OBD2 scanner can check for trouble codes.

2. Poor Performance

Your PCM controls performance, so it makes sense that if it’s not responding correctly, that performance will suffer. The more screwed up your PCM, the more likely you’ll have multiple issues leading to poor performance.

However, if just a single part of your PCM isn’t working correctly, you may only have poor performance under certain conditions, like idling or accelerating.

Related: 8 Causes Why Your Car Won’t Accelerate

3. Probleme Starting

Your vehicle might be impossible to start if your problems with the PCM get too severe. In colder weather, your car might struggle to start.

If your vehicle is having problems starting and it’s related to the PCM, it’s a pretty serious problem that you need to have looked at before you total your engine.

Related: 5 Causes of a Car Engine That Cranks But Won’t Start

4. Surging Emissions

When everything is working correctly, your PCM minimizes your vehicle’s emissions by optimizing performance. When it’s not working the way it should, performance suffers, and you’ll likely have an increase in emissions. However, unless you’re taking your vehicle for an emission test, you probably won’t notice anything different.

5. Poor Fuel Economy

If everything isn’t working correctly, it’s not surprising that your fuel economy will suffer as a result. For instance, you’ll need to accelerate more if your turbo isn’t generating enough boost because the PCM isn’t telling it to.

There are tons of examples like this, but with a faulty PCM, you’ll likely be wasting fuel.

6. Changes in Problems

The problem could be with your PCM if you have difficulty shifting between gears. Your engine, transmission and everything else are controlled by your PCM. So, if you’re having any issues with your powertrain, you might be able to trace it back to the PCM.

If your vehicle is having problems shifting, it’s a severe condition that you need to have addressed immediately. If your vehicle handles erratically it could lead to an accident.

PCM Function

Your engine's power delivery unit is controlled by the PCM. This unit controls several features including the ignition timing and fuel delivery as well as emissions, turboboost pressure, idle speed and throttle control.

While you might’ve heard of Transmission Control Module (TCM) or an Engine Control Module (ECM), a PCM controls both of those functions. A PCM is a unit that houses all of the components within a vehicle. Or, one can control both.

All of these functions are controlled by the PCM through various sensors that can communicate with it. The PCM sends a command to the actuator, and then it measures the results using a sensor.

The PCM is programmed to tell each actuator what to do when specific commands are met – like when hit the throttle – and then it’s programmed to know what the acceptable readings are in response.

When something isn’t working correctly, it shoots a warning to the driver through a check engine light. No, it’s not an easy component to understand, and unless you have the proprietary software, it’s not a component you’re going to fix either.

Locate a PCM

The PCM can be found in either the engine bay or the interior of the car close to the fuse box. Sometimes, it can also be found behind covers under the windshield.

There are a few different locations that the manufacturer can place your vehicle’s PCM, but the most common location is in the engine bay. The PCM doesn’t look like anything special, just a metal box with some wires coming out of it.

If your vehicle’s PCM isn’t in the engine bay, it might be inside the passenger compartment. While this location isn’t all that common if it is there, it is typically underneath the passenger side dashboard – behind all the plastic coverings.

In the ultra-rare instance that your PCM isn’t in either of those locations, it might be in your vehicle’s trunk. This isn’t as common since all of the wires from the engine will have to run to the vehicle’s rear to communicate with the PCM.

Prices for replacing a PCM

The PCM is a computer, and computers aren’t cheap to replace. That’s why the average PCM replacement cost is anywhere between $800 and $1,500, depending on the car model and labor costs.

Worse, the PCM is nearly always more expensive than the labor. Labor costs typically range between $75 to $100. If you believe you can save $100 on labor and have it replaced by yourself, you might be wrong.

That’s because you need to program the PCM to your specific vehicle, and unless you have the proprietary software to do it, you’ll need to take it to the dealership.

The good news is that the dealership will see if they can’t reprogram the PCM before replacing it. If you’re lucky, they’ll find an update and reprogram it for you, which generally only costs between $75 and $150.

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