This code is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model.

The keep alive memory is the memory that is stored in the powertrain control module (PCM) in regards to drive cycles. This memory is ever changing based on driving inputs and sensor inputs. When you disconnect your battery this memory is erased and the computer goes into "dumb" mode as it is using the built in parameters to run the engine and not the learned values based on driving inputs and habits as well as what the engine sensors see.

This is different than "limp" mode as the PCM is not seeing a fault. The PCM memory hasn’t adapted to the needed engine parameters. As stated this is NOT the hard programmed values but the ever-changing values that help for fuel economy, smooth running, easier starts, etc. This data is an adaptive formula used by the PCM to improve engine performance, shift fuel, fuel trims, etc.

Other internal control module error trouble codes include:

Photo of a PCM with the cover removed:

Symptoms of a P0603 DTC will include MIL (malfunction indicator lamp) illumination, although there may be other symptoms including but not limited to engine stall, various warning lights on dash, module communication codes, no start conditions.

Potential causes may include:

This is quite a difficult problem to isolate. In my experience it has been both a wire issue and a PCM issue. It could be interference from a component that fried the PCM.

Inspect the battery cables. It may be as simply as a highly corroded terminal or loose connection. Also check all grounds and fuse box and PCM connections.

Check the charging system. Run the car with the alternator disconnected. There may be interference coming from the alternator. Does the code come back with the alternator disconnected?

Inspect wire harnesses that run close to the ignition system. Interference from these components may be being "thrown" into the circuit. Also check spark plug wires, coil for cracks or anywhere where ignition voltage can "leak".

Using a voltmeter find the power supply circuits to the PCM. Monitor voltages while wiggling, bending, shaking the harness all around the engine and fuse boxes.

In many vehicles the PCM is located in a secluded spot. Meaning there’s a chance that water may have gotten into the PCM case. Also a chance for vibration transfer. If no faults are found there may be an issue with the PCM itself.

Finally, if your vehicle has an aftermarket chip or program in the vehicle, this may be the issue. Also, many manufacturers constantly update the software that is available for your computer, the code may be corrected with a reflash.