This isn't a simple fix and can stem from several issues:
* PCM Failure: The most likely culprit. The PCM's processor may have simply failed due to age, heat, voltage spikes, or other internal component degradation. Replacing the PCM is often the solution, but it requires proper programming to match your vehicle's specifications.
* Power Supply Issues: Insufficient or erratic power to the PCM can cause internal errors. This could be due to:
* Faulty battery: A weak or dying battery can lead to inconsistent voltage.
* Faulty alternator: An alternator not charging properly will also cause voltage fluctuations.
* Wiring Problems: Damaged or corroded wiring to the PCM can disrupt power delivery.
* Ground Issues: A poor ground connection for the PCM can cause similar problems as power supply issues.
* Internal Short Circuit: A short circuit within the PCM itself can damage the processor.
* Software Glitch (less likely): While less common, a software glitch within the PCM *could* theoretically cause this code. A PCM reflash (reprogramming) *might* help in rare cases, but it's less likely than hardware failure.
Troubleshooting Steps (Proceed with caution, working with automotive electronics can be dangerous):
1. Check the obvious: Start by verifying the battery voltage and alternator output. A low voltage can lead to erroneous codes.
2. Inspect wiring: Carefully inspect the wiring harness leading to the PCM for any signs of damage, corrosion, or loose connections. Pay attention to the ground wires.
3. Professional Diagnosis: The best approach is to have a professional mechanic diagnose the problem. They can use a scan tool to get more detailed information and perform tests to pinpoint the source of the issue. A simple code reader might not give all the necessary data.
4. PCM Replacement (If Necessary): If the PCM is faulty, replacement is usually required. This is not a DIY job for most people as it requires specialized tools and knowledge for proper programming. A used PCM *might* work, but it needs to be programmed for your vehicle's VIN or it won't function correctly. A new, remanufactured PCM is usually the safer route.
In short, a P0603 code on a Northstar is serious and usually points to a PCM problem requiring professional attention. Don't attempt major repairs without the proper knowledge and tools.
