How to test PCM with multimeter

Cars produced in the more contemporary years have helped to make our lives a whole lot easier. The electronic components within them have particularly been helpful.

How does a simple push of a button have control over your engine and transmission, among other systems within the car? Well, this is owed to the PCM (Powertrain Control Module).

This article quickly sheds light on some of these issues you need to know and how you could simply use a multimeter to make a diagnosis. Let’s get right in.

What is a PCM on a car?

It is a joint controller for your Engine Control Unit (ECU) and Transmission Control Unit (TCU), two important engine computers. It is also known as the Ignition Control Module (ICM) or the Engine Control Module (ECM).

However, just like every other electronic component, issues with your PCM are bound or expected to arise; some more serious than others.


Symptoms Of A Faulty PCM

Before diving into your car systems to poke hands at your PCM, you have to be rest assured that it does have faults. Here are some of the symptoms to search for that point toward a faulty PCM;

  • Warning lights are on. These include the “check engine” light, the traction control light, and the ABS light.
  • Misfiring or backfiring engine
  • Excessive exhaust and increased fuel consumption
  • Difficulties starting the car as it stutters or entirely fails to start
  • Weak tire controls
  • Poor gear transmissions

These are only a few of the multiple symptoms that come with a bad PCM. Nonetheless, those mentioned above are more common and point you towards a problem.

Testing PCM with multimeter

Now it is understood that a multimeter plays a very important role when testing your PCM. However, it is not the only tool you need. Some of the other important tools to make a proper and comprehensive diagnosis include:

  • A Phillips screwdriver 
  • A flashlight
  • An OBD code scanner, and
  • a new PCM, in case you have to replace the PCM in the worst-case scenario

Generally, a multimeter is most relevant when testing the battery and system wiring for problems. But before you go into these, you have to take preliminary steps;

  1. Make A Visual Inspection

Visual inspections are just checks you do on your engine and systems to quickly search for surface problems. When doing this, you want to pay attention to your wires.

You check to see that your wires are not disconnected and are free from corrosion and rust.

You also check to see that there are no excessive rusts on the battery or PCM itself. Excessive corrosion on the PCM means you may have to replace the whole PCM with a new one.

Once these are checked, you move to the next step, and this is where the multimeter comes in.

  1. Inspect Your Battery

Battery inspection is mainly concerned with your battery charge voltage. A low battery voltage could be the cause of malfunctioning sensors affecting the PCM’s functionality. 

Identifying a problem here saves you a lot of stress.

What you do with a multimeter is check to see that the battery voltage reads about 12.6 volts when the engine is switched off and about 13.7 volts when the engine is switched on. 

In case your result is a negative voltage, here are quick guide on how to fix it.

If the reading goes below the numbers mentioned above, you proceed to charge your battery and test it out again.

While testing your battery, you set your multimeter to 15 volts or 20 volts, depending on what is available on it. You remove each battery plug and then connect your pins to the battery posts.

The red pin to the positive battery post and the black pin to the negative post.

Here is a video that paints a vivid picture of this.

  1. Use An OBD Code Scanner

Once the above steps have been completed with no issues found, your OBD code scanner comes into play.

With an OBD scanner, you test your entire vehicle for OBD error codes. You simply plug it into your vehicle and read for codes.

There are multiple OBD error codes that have different meanings, so you need access to interpretations of these either through a codebook or directly from Google.

OBD error codes provide hints to both mechanical and electrical failures. Retrieving a code that closely relates to your PCM reduces the scope of faults and makes diagnosis a whole lot easier. 

For instance, the P0201 error code indicates that the PCM has a problem with the cylinder 1 injection circuit. This is caused by a dirt-filled fuel injector, a corroded fuel injector, corroded wiring, or poor connections.

Appropriate fixes are then made. 

Alongside P02 error codes, P06 error codes are also common codes that relate to the PCM.

Of course, where the OBD scanner does not provide an error code pointing to your PCM, you change your focus to other parts of your vehicle.

Making use of an OBD scanner isn’t as hard as you may be imagining.

  1. Examine Your Sensors and Wiring

Now, a multimeter is also quite relevant here and things could be a little more complicated compared to previous steps.

Using a multimeter, you inspect sensors connected to the PCM and their associated wiring. You look for bad readings on your multimeter and change any component that seems to be having problems.

You also check your ground wires and every connection associated with them. They are typical culprits.

If problems are seen here and changes to these sensors are made, you then reset your car codes and test that everything is working fine.

What if all these don’t solve your problem?

  1. Replace Your PCM

This is the last step you embark on. Here, you seek professional expertise in replacing your whole PCM and make sure that the new PCM you purchase is specifically compatible with your vehicle.

multimeter and pcm

Does This Fix Everything?

Remember that you have to be rest assured that your PCM is the major culprit. If this is not the case, sadly, problems with your car systems may persist.

Nonetheless, carefully following these steps with a multimeter by your side assures that all problems associated with the PCM are solved.