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P0603 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Internal Control Module Keep Alive Memory (KAM) Error


When a Keep Alive Memory Module (KAM) or power/ground supply is broken, then the P0603 trouble code is triggered. Your vehicle's engine control unit receives information from many sensors on the engine while you are driving. By sensing how you drive, your engine control unit optimizes fuel consumption and timing. In the Keep Alive Memory Module (KAM), these parameters are stored to optimize your fuel economy.


This condition may be caused by many factors, including:

  • Voltage drop on the battery 
  • Batteries connected loosely 
  • Faulty internal memory in the ECM (Engine Control Module) 
  • ECM or PCM water intrusion 
  • The ECM / PCM is not receiving power 
  • An ECM / PCM with a faulty ground wire 
  • Problems with software / reprogramming of ECM / PCM 
  • Charging (faulty alternator system)


With P0603, just like with other error codes involving internal control modules, not only does the Check Engine light illuminate, but other dashboard warning lights as well. These are some other symptoms of this error code:

The symptoms may include poor fuel economy, lag or stalling in the engine, rough idle, low acceleration, and an illuminated service engine light lamp. A pending code will appear if the service engine light lamp has not yet been illuminated and this code is stored.


Checking the battery cables is the first step in diagnosing this problem. Simple corrosion or loose connections may cause the problem. Furthermore, they check the grounds, fuse box, and connections to the PCM.

A vehicle with an alternator connected is then run to verify the charging system. Alternators may cause interference. When the alternator is disconnected, they check if the code returns.

After that, they inspect the wiring harness surrounding the ignition system. This circuit may be affected by interferences in these components. Furthermore, they inspect the coils, spark plug wires and any places where the ignition voltage may leak.

Once the PCM power supply circuits are found, a voltmeter will be used. As they bend, shake, and wiggling the harness all around the engine and fuse box, they monitor the voltages.

PCMs are sometimes located separately in some vehicles. Therefore, there is a possibility that water may have gotten into the PCM, causing it to malfunction. Vibration transfer is also a possibility.

Common mistakes

When a communication failure occurs, symptoms and stored codes are often misdiagnosed and repaired as if they were the cause. This results in a failed repair. It is possible that codes related to engine malfunction, exhaust leaks, fuel injectors, and any other transmission or drivability issue that may be coupled with a controller communication code can lead to incorrect diagnosis. When you diagnose codes based on their order of storage, you will increase your chances of making a successful diagnosis. You can determine which code was stored first by using freeze frame data.

What repairs can fix the code?

The following are common fixes for this error code:

  • Make sure you have a fully charged battery before you take any measurements.
  • Make sure the cable connections are not damaged or corroded.
  • Ensure that all wires entering the wiring harness are in good condition.
  • Examine all wiring leading to and from the engine control module.
  • The engine control module is supplied by wires that must be tested for voltage. Wiring instructions and voltage readings are provided by your service manual.
  • If there is any evidence of water intrusion, the engine control module can become damaged.
  • Even if the defects seem minor, you should replace or repair any faulty wiring.
  • Look for signs of faulty wiring around the engine control module if you don't see any.

Related codes

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


If your vehicle’s engine control unit senses that the Keep Alive Memory Module (KAM) has been broken, then it will trigger the P0603 trouble code. These modules are energy-efficient and are designed to store engine parameters during the vehicle’s idle time. Don’t let your engine control unit sense that your KAM has been broken – fix it with a replacement and don’t let the P0603 trouble code get triggered.