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P0404 OBD2 Fault Code on 2003 Pontiac Grand Prix 3.1L Engine - Diagnosis and Solutions

Model: Pontiac Grand Prix Fault Code: P0404 Posted: 2016-08-04 12:39

I'm experiencing a P0404 diagnostic trouble code on my 2003 Pontiac Grand Prix equipped with the 3.1L engine. Despite replacing the spark plugs, ignition wires, EGR valve, and mass air flow sensor, the vehicle still lacks power—especially in low gears—and feels as though one cylinder is misfiring. I've tested all ignition coils and confirmed they are functioning properly. The catalytic converter was removed and inspected; it appears intact with no visible damage or failure signs. I'm seeking advice on how to resolve this issue, particularly since the P0404 code persists even after these repairs. Could the problem be related to fuel delivery, sensor accuracy, or a deeper system malfunction? Any guidance on next steps would be greatly appreciated.

Related fault codes
P0404
Comments (4)
Anonymous 2016-08-04 16:16

This is a 3.8L engine without a supercharger? First, ensure the catalytic converter is properly replaced and then post all OBD2 codes. Confirm your electrical troubleshooting using wiring diagrams and a digital multimeter (DVOM).

Anonymous 2016-08-08 07:21

It's actually a 3.1L engine with no supercharger. I removed the catalytic converter, opened it up, and inspected it—no signs of failure or blockage. My electrical troubleshooting has been minimal; I haven- t used wiring diagrams or a DVOM for in-depth diagnostics.

Anonymous 2016-08-19 20:29

Could you please advise whether I should install an OEM catalytic converter or any compatible replacement to clear the P0404 code? What are the risks of using non-OEM parts?

Anonymous 2016-08-20 08:03

Teasley32 — consider starting a new topic and providing full vehicle details, including all OBD2 codes, symptoms, and diagnostic steps. For reference, see: http://www.obd-codes.com/forums/posting.php?f=19