P0603 Code – Meaning, Causes, Symptoms (& How To Fix It?)

What does the P0603 code mean?

The P0603 error code is triggered when an internal error occurs in the Keep-Alive Memory Module (KAM) or the current/ground supply is faulty. While you are driving the vehicle, your engine control unit receives information from many sensors on the engine. The engine control unit senses how you are driving your car and uses this information to optimise fuel and timing. The KAM is used to store these parameters to optimize fuel consumption and other optimizations while driving.

Definition: P0603 OBD2 Code Internal Control Module Keep Alive Memory Error

The P0603 error code is a general error code that applies to all makes and models from 1996 onwards.

If you disconnect a battery terminal and cut off the power to the KAM memory, the KAM memory is erased and the vehicle returns to standard mode without the optimizations and must be restarted to learn it again. Each time you start your vehicle, the engine control unit attempts to read the memory from the KAM. If it cannot read the memory for a number of attempts, it triggers the P0603 error code. If your vehicle receives P0603, your engine runs in standard mode and does not optimise/learn from your driving style.

Other related trouble codes may be:

• P0601 – Internal Control Module Memory Check Sum Error
• P0602 – Control Module Programming
• P0604 – Internal Control Module Random Access Memory
• P0605 – Internal Control Module Read Only Memory Error

P0603 Symptoms

The symptoms of P0603 are usually just the check engine light coming on and your car possibly not starting. The vehicle may also have no symptoms if the code is stored and the fault occurs intermittently. You may also get several different symptoms of the P0603 code, such as:

• The car doesn’t start or hard starting conditions
• Check engine light or service engine soon light ON
• Other warning lights may illuminate
• Misfiring
• Rough acceleration
• Rough idle
• Erratic shifting

Possible P0603 Causes

The most common cause of this error code is the ingress of water that damages the ECM. There could also be a short circuit in a cable in the engine control unit that has blown internal parts in the PCM/ECM. You should always check and measure all cables before replacing your engine control unit because if the short circuit is still present, you could also damage your new ECM/PCM.

• Low battery voltage
• Loose battery terminal connection / Poor connection
• Internal memory fault in Engine Control Unit (ECM) / Powertrain Control Unit (PCM) (Keep Alive Memory Module (KAM))
• Water intrusion in the ECM / PCM
• Faulty power supply to ECM / PCM
• Faulty ground wiring to ECM / PCM
• Software fault / Programming of ECM / PCM
• Charging (Alternator system faulty)

Possible P0603 Solutions

• Charge your car battery and erase trouble codes.
• Check for loose or poor connections on both battery terminals
• Check all fuses
• Check ground between the battery and body
• Check the charging voltage with a Digital Multimeter (Should be over 14 volts at idle)
• Check the power supply to ECM/PCM
• Check ground to ECM/PCM
• Check for water intrusion or corrosion inside ECM/PCM
• Check for Corrosion in ECM/PCM Connector
• Replace ECM/PCM if faulty

How to diagnose the P0603 code

This is a guide to how a professional automotive technician might resolve this problem. It may require some knowledge of car electronics and you will need some tools, but it can help you even if you have little knowledge of cars. Always connect a car battery charger when performing a diagnosis on your car. A low voltage can trigger other error codes and even damage control units.

1. Visually inspect the battery terminal connections and check if they are loose. Check the ground wire between the battery and the casing. Clean it if you find corrosion or a bad connection. Clean the grounding points and clean the ECM connector.
2. Connect a car battery charger to your battery and make sure it is charging your battery. Let it charge for a while.
3. Connect an OBD2 code scanner to your vehicle and verify the P0603 code. Erase the code and restart the ignition. Check if the trouble code is coming back. Take some test drives to see if the problem is gone or if the P0603 keeps coming back. If the problem still occurs, continue the troubleshooting.
4. Measure the voltage between the battery terminals at idle (>14 volts) and with the engine off (>12 volts) with a Digital Multimeter. Replace any damaged fuses.
5. Disconnect the ECM/PCM connector and get a pinout diagram of the ECM connector. Measure that you have 12 volts on all power supplies and check that the grounding pins are OK. Check for possible short circuits.
6. Open the engine control unit and check for any visual damages or water infiltration.

If all power supplies, ground wires, battery, or alternator voltage tests are okay and you can’t find any short circuits, it may be an internal fault in the Engine Control Unit. You could either let an electronic expert take a look at the engine control unit or replace the ECM/PCM.

Note: In newer vehicles, an immobilizer is usually integrated into the ECM, which you cannot replace without programming. Some engine control modules can only be programmed once for a vehicle. If you buy a used control unit, you cannot reprogram it again. However, some small workshops have tools to re-program them, but this requires some extra work. Buying a new engine control unit is always the easiest choice. Before installing the new ECU, always read the old parameters from the old ECU.

Recommended Tools to Fix P0603

These tools are from Amazon and are recommended for a proper diagnosis of your vehicle.

• OBD2 code scanner to read the trouble code memory. To reprogram the new ECU, you need a more advanced OBD2 scan tool.
• Always charge your car with a Car Battery charger while doing any work on your vehicle.
• A Digital Multimeter is required to measure the power supplies and ground wires and it will make the troubleshooting a lot easier.

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