1997 Cadillac DeVille P0603 and P1604 Fault Code Diagnosis - Fuel Pressure & Engine Misfire Issues
Hi, I own a 1997 Cadillac DeVille with a 4.6L engine. The car runs smoothly under light throttle but exhibits rough running, misfires, and backfiring when under load. These symptoms resolve within seconds, after which the vehicle returns to normal operation. Previously, no PCM codes were present, but after the battery died during a long idle period, two fault codes appeared: P0603 and P1604. I'm wondering if low fuel pressure could be causing these issues—though I've never seen low fuel pressure trigger a code before. What should the proper fuel pressure be for this model? Any insights into potential causes or diagnostic steps would be greatly appreciated. Thanks, Mike and the sweetest mechanic's helper you've ever seen!
Low fuel pressure could be a contributing factor, but it’s not the only possibility—many other issues can cause similar symptoms. I’d recommend checking the ignition system components, including spark plugs, wires, and coils, as faulty ignition parts may lead to misfires and backfiring. The P0603 code typically indicates an issue with memory or data storage in the PCM, while P1604 points to a problem with the engine control module (ECM) or related sensors. Given that the battery died during idle, it’s possible voltage fluctuations affected system stability. A thorough diagnostic scan and component testing are advised. Thanks for sharing—keep me posted! Jeff