What is the P0603 Code? Meanings, Causes and How Do You Fix It?

It's easy to wonder how hard it will be for you to get the code P0603 on your OBDII scan. In some cases, it’s an easy fix, but it can also be something complicated. 

That’s why it’s important to figure out the P0603 meaning and examine the causes. The P0603 symptoms will be examined and possible solutions provided. 

Definition of the code P0603

P0603 – Internal Control Module Keep Alive Memory (KAM) Error

What does the P0603 code mean?

P0603 is a generic code that indicates the Powertrain Control Module's (PCM), failed to pass the Keep Alive Memory self-test. This is necessary to store all driving information, such as engine timing and ignition, for the transmission. 

PCM controls many systems within the car. It’s programmed to have factory default settings, but these aren’t always ideal for your driving style. The PCM adjusts these settings over time to make the car more suitable to your driving style. 

The PCM saves these settings instead of having to change them each time you start your car. If the settings can’t be retrieved when you start the car, the P0603 alerts you to trouble. 

RELATED: 6 Symptoms of a Bad PCM (& Replacement Cost)

P0603 Trouble code symptoms

Check Engine Light is the most frequent symptom of P0603 codes. Other symptoms include difficulty starting your engine or performance problems.

Below are the top symptoms.

• Verify Engine Light
• It is difficult to get the engine started
• Idling/rough acceleration
• Shifting issues
• Mistakes
• Stalling

The P0603 Code: Causes

P0603 could be due to simple electrical issues or malfunctioning sensors.

Below are the top causes.

What is the P0603 code?

High – In some rare cases, you might notice any other symptoms with the P0603 code, but that’s not normally what happens. The KAM stores the performance settings so if the KAM is not working, acceleration, idle, and start can be affected.

Even though your car may run well initially, problems can quickly arise when you're away. You can avoid becoming stranded at a remote place by quickly fixing the issue. 

How can you fix the P0603 codes?

These are some possible fixes that could resolve P0603 code. It is important to perform a thorough diagnostic before you replace expensive parts.

• Re-establish connection by cleaning out battery corrosion
• Replace defective KAM wiring
• Replacing the PCM

Common mistakes in diagnosing P0603

Many people jump right to replacing a PCM that isn’t defective. While performance issues may seem to be the main problem, it could also be other smaller problems. 

You don’t want to replace the PCM when the root problem comes down to a bad connection. Replacing a battery or checking the wiring is a much easier and less expensive fix, so that’s where you should start. 

Recommendations for Diagnosis

How do you diagnose the P0603 Trouble code?

It’s not always easy figuring out the P0603 code, but these steps can set you on the right path.

1. You should start with a fully charged cell.
2. Examine the connections and terminals for signs of corrosion. Verify that everything has a tight connection.
3. Verify the wiring that goes into the fuse box wiring. Replace any damaged wires.
4. Make sure you inspect the electrical wiring that connects to the PCM. Replace anything that is broken.
5. You can measure voltage from the PCM. This should help you to understand how to measure voltage going to the PCM. 
6. Check for water signs near the PCM. Any type of intrusion could cause the module to be damaged.
7. The module should be flashed and the default settings set. You can test the module again by driving the car. 
8. You can replace the PCM. 

The estimated cost of repair

Repairing the P0603 code is expensive. It can cost anywhere from few dollars up to hundreds. 

• Battery Corrosion Cleaning – the cost of supplies
• Replace wiring – $50-$1,000
• Replace PCM – $700-$1,500

Here are some mechanics tips about the P0603 code

You could have problems with an aftermarket tuneer. Remove the tuner from the vehicle and check if it is still there.

Additionally, it’s possible to see other trouble codes with the P0603 alert. Below are some possible examples:

• P0607 – Control Module Performance error
• P0605 – Internal Control Module Read Memory (ROM) Failure
• P0604 – Internal Control Module Random Access Memory (RAM) Error
• P0601 – Internal Control Module Memory Check Sum Error
• P0600 – Serial Communication Error

These trouble codes are P0603-related. You need to first fix and troubleshoot them. Each of these could solve the problem, or at most help you find it.