How to Test PCM with Multimeter

How to Test PCM with Multimeter: Step-by-Step Guide

Most modern vehicles come with many components that need to work harmoniously for the vehicle to work correctly. When you first get the vehicle, it will function so great that you will not have to worry about anything. But with time, it is understandable that some parts may malfunction and need to be repaired or replaced.

One of the essential parts of each vehicle is the PCM. In today's guide, I will cover everything you need about this part. I will give you a step-by-step guide to teach you how to test a PCM, what equipment to use, and how to know if you need to repair or replace the PCM.

If this is something that you are interested in, stick around for the rest of the guide. Let's get right into it!

What is PCM?

Car PCM Powertrain Control Module

The first thing you need to know is what a PCM is. PCM stands for Powertrain Control Module, a combination of a vehicle's engine and transmission control modules.

This vehicle part is most important as it is the car's brain. It has the critical task of monitoring and managing engine performance. So, it takes data from all component parts in the vehicle and processes it to help you achieve optimal driving performance.

If you have a faulty PCM, you will immediately be able to notice a change in the functioning of your car. Some of the common characteristics of a defective PCM include the following:

Incorrect codes will start appearing on your dashboard, including a Check Engine light that will constantly be on.

You might have difficulties starting the car, whereas after starting it, you might have problems changing gears or speed.

Fuel consumption will increase even if you do not change how you drive your car.

Often engine misfires are also possible when you deal with a PCM failure.

You may have a bad PCM if you encounter any of these problems while driving your car. You can either seek professional help from the get-go or test the PCM yourself to see if you can detect the issue. If you decide to try testing PCM on your own, make sure you read the step-by-step guide given further below.

What You'll Need to Test PCM with Multimeter

If you try researching how to test a PCM, you will find various guides about testing car parts, batteries, wires, etc. Instead of using multiple tools and wasting precious time, I recommend testing your PCM with a multimeter. It is the quickest and most efficient way to detect PCM problems.

The testing is not that difficult, but it does require a few appropriate tools. I recommend that you always have a multimeter, a flashlight, a few screwdrivers, the multimeter probes, an OBD code scanner, and a replacement PCM in case you need to replace your old one or do some tests.

Furthermore, I recommend that you wear safety glasses while doing the testing. That way, you can protect your eyes in case something goes wrong. After gathering all your equipment, you can start with the PCM testing!

Step-by-Step Guide to Test PCM with Multimeter

PCM multimeter

After you gather all the needed gear, you can start testing the powertrain control module. It is wise to follow a manual or guide on how to do this. If you do not have any previous experience with car testing, it might also be wise to seek professional help.

Should you decide to do the testing yourself, get your car, pop the hood, and let's get started with the testing:

Step 1 - Do a Visual Inspection

Sometimes, changes in how your car functions might not be caused by the PCM but by loose wires or connections, some rust or corrosion, some loose pins, etc. So, it is wise to do a visual inspection before you do anything else.

Look at the engine and find the PCM. Look at the surrounding area and check for any visible problems. If there aren't any loose connections or rust, chances are there are some mechanical issues with the PCM. So, you should proceed to the next step to find what is causing your car's poor performance.

Step 2 - Check the Battery Voltage

Next up, you should check the battery voltage. More often than not, a weak battery can cause your car to malfunction or show error codes. Since testing the battery is quite easy, you should start with that.

Find the car battery and connect the multimeter probes to it. The multimeter should be set to volts and show a voltage reading as soon as you connect the battery.

When the vehicle is off, the voltage should be around 12.6V. If you turn the car on, the voltage should rise to 13.7V. If you see that the voltage drops after turning the car on, chances are some component part is causing a problem.

A high voltage drop does signify that there is a problem with the PCM. But if the voltage is not where it should be from the get-go, you are likely dealing with a weak battery. There is an easy fix for this - you can use a car battery charger to recharge the battery within a few hours.

If that does not help, you can replace the battery with a new one. Then, test the voltage drop to see if the same problems appear. If it does, move on to the next step.

Step 3 - Do Code Scanning

If the problem is not a weak battery or corrosion, you can also use an OBD code scanner to find the problem. All you need to do is connect the scanner to the car and allow it to check which parts are working fine and which are faulty.

If there are any faulty parts in the car, the scanner will show a code that tells you what needs repairing. All OBD error codes point to a specific car problem, so you can locate and repair the problem quickly. You can check your code book or search for information on the code online.

Step 4 - Test Separate Components

If you do not have an OBD scanner, you can always test separate components with the multimeter. This will be more time-consuming, but it is what you must do to locate the problem.

You can test wire continuity by attaching the multimeter to the PCM power circuit and setting it to ohms. If the multimeter shows "0," the car has no continuity problems. If it shows any other number, there might not be sufficient current going through the wires.

You can also test the resistance in the same way. The only difference is that the multimeter should be connected to each part connected to the PCM power circuit. The separate parts should have less than a double the recommended resistance value. You can check the recommended value for each element in the car's manual or online.

Finally, you can connect the multimeter to each part separately to check the voltage. Know that you have located the problem if you find a significant difference in the voltage shown on the multimeter and recommended voltage for that part.

Step 5 - Replace or Repair

After testing the PCM with a multimeter, you can tell whether the part is beyond repair. If you can repair the PCM, take the car to the mechanic's shop to have it repaired. It would be best not to fix it alone, as even the slightest problem could lead to total car damage.

If the PCM is beyond repair and the mechanic confirms that, get a new PCM and install it in your car. Then, do the voltage test and see if the car works well. If there is still some problem, you might be dealing with a problem with the ignition system, fuse box, sensors, transmission, etc.

Troubleshooting PCM Issues

When testing a PCM with a multimeter, you can detect many issues with separate car parts or the PCM itself. By just looking at the car engine and PCM, you can see if there are faulty ground wires or excessive corrosion that might be causing your car to malfunction.

Aside from wire and corrosion problems, another common you can detect with a PCM test is a battery problem. Low voltage can cause several issues, so always ensure your vehicle's battery is fully charged.


Thank you for reading this guide on testing a vehicle's powertrain control module. Remember that you can detect many issues by doing this simple multimeter test. While you can do the test yourself, you should leave all repairs and replacements to the professional mechanics.

If you have any experience with PCM failure or testing, please share it with me in the comments below. Let me know how you handled the problem and what steps you recommend others follow when doing the same tests. I cannot wait to read your comments!

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