Error Code P0603 is defined as Internal Control Module Keep Alive Memory (KAM) Error. This means the PCM is working on its default parameters, rather than with the information stored from drive cycles.

This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs of course, vary from one make and/or model to another.


The PCM (powertrain control module, also known as ECM or engine control module) in cars are sophisticated computers responsible for controlling of all electronic components concerned with the vehicle’s operation, such as ignition timing, fuel mix, etc. It also stores information when the vehicle is being driven, and it “learns” how you drive and suit the vehicle’s performance to match your driving needs, as well as the conditions where you drive it. This is referred as the KAM or the Keep Alive Memory. The memory changes based on the driver and sensor inputs. Disconnecting the battery will erase all the memory, putting the PCM into “dumb” mode, and will use the built-in or default parameters to run the engine, and NOT on the learned values based from the driving inputs, what sensors sees and driving habits.

When Error Code P0603, it means there’s an error in the PCM’s operation of the KAM, and is running in default parameters rather than using the information from stored drive cycles.

Other related internal control module error codes include:

Common Symptoms

As with other error codes that concerns the internal control module, P0603 triggers not just the Check Engine light, but also other warning lights on the dashboard. Other symptoms of this error code include:

  • Hard starting or no start conditions
  • Engine stalling
  • Harsh or erratic shifting in transmission
  • Decrease in fuel economy
  • Dying when coming to stop
  • Misfire-like conditions

In some cases, there may be no observable drivability symptoms.

Possible Causes

There are many factors that may cause this condition, such as:

  • Corrosion in the battery terminal
  • Loose connections in the battery terminal
  • Keep Alive Power (KAPWR) circuit wire routing
  • Charging system fault Ignition system fault causing secondary ignition voltage inference
  • Open wire in the KAPWR circuit
  • Damaged PCM, water intrusion / internal fault
  • Internal PCM program fault

How to Check

To diagnose this problem, technicians start by checking the battery cables. The problem may be caused by as simple as loose connection or corrosion on the terminal. Also, they check all grounds and fuse box and connections to the PCM.

Next, they check the charging system and run the vehicle with alternator connected. There may be interference coming from the alternator. They check whether the code comes back with the alternator disconnected.

Next, they check the wire harness that runs close to the ignition system. Interferences in these components may be thrown into the circuit. They also check the coil for cracks, spark plug wires, or anywhere that may be leak in the ignition voltage.

Then they will use a voltmeter to find power supply circuits to the PCM. They monitor the voltages while bending, shaking, wiggling the harness all around the engine and fuse boxes.

In some vehicles, their PCM is secluded in a separate spot. Which means there’s a good chance water may have gotten into the PCM, causing the problem. Also, there could be a chance for vibration transfer.

If after all these diagnosis no faults are still found, then it may be a case for damaged PCM.

Lastly, the vehicle may be using an aftermarket chip or program which may be causing the problem. Also, many vehicle manufacturers provide updates for the computer, and a reflash may correct the error code problem.

How to Fix

Here are common fixes for this error code:

  • Replacing damaged or faulty connectors, components or wirings, and make sure all connectors are secured
  • Replacing of faulty components in individual control modules
  • Replacing faulty PCM

Dumb mode and “Limp” mode are two very different faults. The memory of the PCM has not adapted to the needed engine parameters. It’s not the case of hard programmed values, rather, the ever-changing values that help for better fuel efficiency, smoother run and easy starting. The information from the KAM is an adaptive formula used by the PCM to improve its engine performance, fuel trims, shifting fuel, etc.

One of the most common misdiagnosis of this code is replacing the PCM when the cause of the problem is simply improper voltage to the PCM KAM circuit. Also, some people replace the PCM entirely, when the problem is a case of defective PCM ground circuits.