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P0603 Code: What It Means and How to Fix It

A P0603 code is one of many universal error codes that your car may generate. If you see this code on your code scanner, it could mean anything from the minor inconvenience of replacing your battery to serious powertrain problems like mistimed shifting.

In this article, we’ll discuss possible causes of the P0603 code, how to make a diagnosis, and how to repair your car.

Tools Needed For Diagnosis and Repair

In order to diagnose and repair a P0603 code, you’re going to need a few tools. Have the following things ready before you begin:

  • – A flashlight or shop light so you can see what you’re doing
  • – A car battery charger
  • – A multimeter
  • – An OBD2 code scanner

What is the P0603 Code?

The P0603 code indicates that your Powertrain Control Module (PCM) has failed its own Keep Alive Memory (KAM) self-test. The PCM is a computer in your car that controls a variety of essential systems, such as the ignition, engine timing, fuel/air mixture, transmission, and anti-lock breaks.

When a car is manufactured, the PCM is programmed with factory default settings for that model. However, these defaults aren’t always optimal. Depending on your vehicle’s individual quirks, typical road and weather conditions in your area, and your own driving habits, the PCM needs to make adjustments in order for your car to perform optimally.

Rather than make hundreds of tweaks every time you drive, your PCM keeps its settings saved in Keep Alive Memory. If your PCM is unable to retrieve these settings after several attempts, it generates a P0603 code.

What Does the P0603 Code Mean For My Car?

This depends on what the exact differences are between your PCM’s factory default settings and the new settings it’s created. Because cars change as they age, older cars tend to require more adjustments to these settings. As a result, the older your car is, the more severe your problems are likely to be.

The most serious problems are with the fuel/air mixture, engine timing, and transmission. Fuel/air mixture problems can cause your vehicle to lose fuel efficiency and may result in a failed emissions inspection. Engine timing errors can cause the same problems and can cause unnecessary wear and tear on the engine itself. And bad transmission settings can lead to inefficient or rough shifting.

diagnosing p0603 code under the car bonnet

Common Causes of the P0603 Code

There are a few things that can cause your PCM’s settings to fail to load. Here are the most common reasons:

  • – Your KAM is not receiving sufficient power
  • – The KAM or battery ground has shorted out
  • – Your KAM module itself has failed

Common Symptoms Associated With the P0603 Code

If your code scanner is reading a P0603 code, you may or may not be experiencing any other symptoms. These include:

  • – Your check engine light is on
  • – Your engine is difficult to start
  • – Rough idling and acceleration
  • – Badly-timed shifting
  • – Engine misfires

Some of these symptoms are similar to what you’ll see in a car with a failed Transmission Control Module (TCM), so diagnosing based on symptoms alone can be difficult. This is why it’s so important to use a code scanner.

What Does Diagnosing the P0603 Code Entail?

There are a few steps involved in fixing a P0603 code. We’ll start with the easiest ones, and work from there.

Mechanic opening yellow car bonnet

Check Your Battery

Use a multimeter to check your battery’s voltage. If the voltage is low (below 14 volts at idle, or below 12 volts with the engine off), connect a car battery charger and let it charge until it’s full. Then, reset your codes and wait for a few days of normal driving. If the code reappears, you may need to replace your battery or alternator.

If the battery voltage is normal, connect the battery charger anyway. You want to ensure that your battery remains fully charged during the rest of your diagnosis.

Inspect Contacts and Ground Connections

If you’ve gotten this far, your battery itself isn’t the problem. The next step is to perform a visual inspection of your battery contacts. Look for moisture, corrosion, dirt, or anything else that could be causing your car to receive low voltage. If you find anything, clean it thoroughly.

Next, disconnect your PCM, and test all connections to and from the battery. Test the ground connections from your PCM and battery as well, to ensure that they’re not shorted out or corroded. Replace any bad wires, reset your codes, and drive for a few days to see if the code reappears.

If you’ve taken all of these steps and you still need a P0603 code fix, you need to replace your PCM. Our PCM replacement guide explains this process in more detail.

Common Mistakes When Diagnosing the Issue

  • – Failing to check idle voltage and ground connections

Possible Solutions For Fixing the P0603 Code

  • – Try Replacing your battery or alternator
  • – Replacing failed PCM or battery grounds
  • – Consider Replacing your PCM

How Can We Help?

If worse comes to worst and you need to replace or repair your PCM, contact us on our website, or call us at 888-848-0144. Our knowledgeable technicians are specialists in PCMs, and can answer any questions you may have.

Solo PCMS is a national provider and repair center for PCM, ECM, ECU, TCM, and TCU auto computers.
14361 SW 120th Street Unit 106
Miami, FL, 33186, United States