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1999 Cadillac DeVille Northstar Engine Code P0603: Electrical Issue on Driver Module

Model: 99 Cadillac DeVille Fault Code: P0603 Posted: 2016-09-02 17:28

The Engine Control Module (ECM) has detected an electrical condition on the driver module, resulting in Diagnostic Trouble Code (DTC) P0603. This code indicates a loss or unintended change in data within the PCM's keep-alive memory, which can be caused by interrupted power or ground signals to the PCM. P0603 is typically triggered when there is an interruption of 12V power or ground connection to the Powertrain Control Module (PCM), either due to a dead battery, faulty wiring, or internal PCM failure. The issue may also arise if additional electrical devices—such as remote starters—are drawing excessive current. To troubleshoot: - Verify that the PCM is receiving proper 12V power and a solid ground. - Check fuse 10A (Battery) in the fuse box, located at the PCM connector C1, terminals 61 and 20. - Ensure no aftermarket electrical devices or remote starters are interfering with the system. If the problem persists after checking wiring and power, it may indicate an internal fault within the PCM itself.

Related fault codes
P0603
Comments (3)
Anonymous 2016-09-03 07:14

The PCM can experience a loss of power or ground interruption, leading to P0603. This could stem from a dead battery, loose wiring connections, or a complete power cut. Even after replacing the battery and disconnecting the system, if the issue returns, it may point to an internal PCM failure. A 12V or ground interruption will produce the same symptom.

Anonymous 2016-09-09 02:58

My battery cable was loose again—after fixing it, the P0603 code returned. I had a technician reset the system, but all dashboard lights suddenly turned on. This is very frustrating! How can I fix or replace the PCM? Is there a way to avoid this recurring issue?

Anonymous 2016-09-09 09:44

Before concluding that the PCM itself is faulty, confirm that both power and ground connections are stable. You mentioned dashboard lights turning on—did you verify that only P0603 is present? DTC P0603 monitors the PCM's keep-alive memory for data loss or corruption. If such a condition occurs, it sets the code. Begin with a wiring diagram check: inspect fuse 10A (Battery) in the fuse box and ensure proper connection at the PCM connector C1—terminals 61 and 20. Be cautious of any added electrical devices or remote starters that could draw current and interfere. Please confirm these details so we can provide more targeted advice.