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2002 Pontiac Grand Prix GT 3.8L - P0442 and P0404 Codes: EVAP Leak & EGR Valve Issues Explained

Model: 2002 pontiac grand prix gt 3.8 Fault Code: P0404 Posted: 2013-07-23 15:06

Hello, I've been experiencing issues with my 2002 Pontiac Grand Prix GT 3.8L over the past few days and am seeking advice from experienced owners or mechanics. I'm currently seeing two diagnostic trouble codes: P0442 and P0404. P0442 (EVAP System Small Leak Detected): - This code has been present for some time. I initially suspected a faulty gas cap, as there have been no noticeable performance issues. I've tried turning it off temporarily, but the code returns consistently. P0404 (Catalyst System Efficiency Below Threshold): - Over the past few days, my car has shown reduced acceleration and lack of engine power. A local transmission specialist tested the vehicle and confirmed that the transmission is functioning properly. He concluded that the issue lies with either the EGR valve or the catalytic converter. My questions: 1. Are P0442 and P0404 related in any way? Could their presence point to a shared underlying cause? 2. Between these two, which should I prioritize fixing first? 3. Is there a cost-effective solution—such as cleaning the EGR valve or replacing components—before committing to full part replacements? I have basic knowledge of automotive systems but am still learning. Any insights or troubleshooting steps would be greatly appreciated.

Related fault codes

P0404P0442

Comments (5)

Anonymous 2013-07-24 09:59

Address P0404 first—it indicates an EGR valve issue where the Powertrain Control Module (PCM) detects the valve is open when commanded to close. This directly correlates with poor acceleration. P0442 points to a small leak in the EVAP system. Have you replaced the gas cap? If not, that's a likely starting point.

Anonymous 2013-07-24 12:41

Not yet. I cleared the codes and plan to replace the gas cap as a first step. However, I'm considering cleaning the EGR valve before replacing it to avoid unnecessary expense.

Anonymous 2013-07-24 12:59

A scan tool is highly recommended for diagnosing these codes accurately. Check the EGR pintle for carbon buildup or obstruction—this can prevent proper seating and cause the EGR valve to remain open, triggering the P0404 code.

Anonymous 2013-07-27 07:00

I don't believe the P0404 code directly causes low engine power. It's actually an EGR position sensor code for a linear electronic EGR valve with five wires: two for solenoid control and three for valve position feedback via potentiometer. The PCM expects a specific voltage signal from the valve. To test, remove the valve and use a flat-head screwdriver to manually push the pintle back and forth—there should be smooth movement. Also, clean the pintle seat area with a screwdriver to remove carbon deposits that may keep the valve open. For P0442, a smoke machine is ideal for detecting small leaks in the EVAP system. While replacing the gas cap helps, it often doesn't resolve the issue—inspect all EVAP hoses for tiny holes or tears (like finding a needle in a haystack). I personally use a smoke machine and find it very effective.

Anonymous 2013-08-03 15:45

I took my car to another shop for a second opinion and had a compression test performed. The diagnosis revealed that the catalytic converter was clogged, which caused back pressure and triggered both codes. After replacing the cat, engine performance returned to normal. I also replaced the gas cap, and no diagnostic codes have appeared since.