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2002 Impala 3.4L V6 No Start After Replacing EGR Valve with P0404 Code

Model: 2002 impala Fault Code: P0404 Posted: 2018-07-17 18:48

Hello, I own a 2002 Chevrolet Impala with a 3.4L V6 engine. I recently replaced the EGR valve due to a check engine light triggered by code P0404 (Exhaust Gas Recirculation System Flow Malfunction). After installing the new EGR valve, my car will no longer start at all. This is my daily driver, so any help would be greatly appreciated. I’ve tried various troubleshooting steps but haven’t been able to resolve this issue. The vehicle previously ran fine before the EGR replacement. I’m concerned that the installation process may have caused a wiring or electrical fault, especially since the car now fails to start entirely.

Related fault codes
P0404
Comments (18)
Anonymous 2018-07-18 18:51

Try re-installing the original EGR valve and see if the vehicle starts. This can help determine whether the new valve is causing the no-start issue.

Anonymous 2018-07-18 19:37

Did you clear the fault codes after replacing the EGR valve? Check if the P0404 code returns when the engine is running or during a diagnostic scan.

Anonymous 2018-07-18 19:41

I figured out what happened — while removing the EGR valve, I accidentally unplugged the ignition coil. After reconnecting it, the car started normally. This highlights how easy it is to overlook small connections during maintenance.

Anonymous 2018-07-18 19:42

I'm still experiencing hesitation and a lack of power, especially when driving uphill or on inclines. Could this be due to bad fuel or a clogged fuel filter? I’m considering these possibilities.

Anonymous 2018-07-19 07:15

Try using a high-quality total fuel system cleaner like Techtron. If hesitation is present, note how severe it is and whether the P0404 code has cleared after treatment.

Anonymous 2018-07-19 09:58

The P0404 code has returned. The hesitation becomes very noticeable once the engine warms up — especially when climbing a slight incline, where the engine shudders noticeably.

Anonymous 2018-07-19 19:42

Are you experiencing hesitation or reduced power? Clarifying this helps narrow down whether it's an EGR-related issue or something else in the fuel system.

Anonymous 2018-07-19 19:57

The hesitation and P0404 code returned after replacing the EGR valve. This suggests a possible connection between the new valve installation and the symptom recurrence.

Anonymous 2018-07-20 05:21

You previously said the P0404 code was gone, then stated it came back after installing the EGR valve. Do you currently have the P0404 code active?

Anonymous 2018-07-20 06:40

Did you experience hesitation problems before the check engine light illuminated? This could help determine if the issue started post-EGR replacement.

Anonymous 2018-07-20 06:48

No, I did not have hesitation prior to the MIL coming on. However, I still see the P0404 code. My theory is that disconnecting the battery reset the PCM, causing the code to reappear. I suspect bad fuel — I filled up during an emergency situation when the tank was being refilled, which is something I normally avoid. I’m now considering running a water remover (like heat or drip gas) and replacing the fuel filter.

Anonymous 2018-07-20 07:34

Excessive exhaust back pressure could potentially cause this issue. Try disconnecting the negative battery terminal for 10 minutes, then reconnect it and take a test drive. The EGR valve's closed voltage is learned by the PCM — replacing the valve may not update the memory correctly. This suggests an electrical circuit problem, such as carbon buildup on the EGR pintle or issues with the three-wire position sensor (5V reference, ground, signal) from the EGR to the PCM. I’ve never seen P0404 linked directly to combustion problems. If you disconnected the battery, do you still experience hard starting?

Anonymous 2018-07-20 07:48

I occasionally have a hard start — not consistently, but sometimes when cold or after long periods of inactivity.

Anonymous 2018-07-20 08:10

Auto Joe: After replacing the EGR valve, I disconnected both battery terminals for about an hour. On Tuesday, no codes appeared. However, on Wednesday, no issues were noticed — by Thursday, the P0404 code returned along with the hesitation symptoms described earlier.

Anonymous 2018-07-20 08:16

It's strange that both the P0404 code and hesitation occurred simultaneously after a fueling event. I wouldn’t expect fuel quality to directly affect P0404, but it’s worth considering. Perhaps the new EGR valve is faulty — consider returning it for a replacement. A proper scan tool would be needed to test EGR circuit functionality with bidirectional controls and monitor EGR position feedback to the PCM.

Anonymous 2018-07-20 08:18

If the PCM receives incorrect feedback from a defective EGR valve, this could explain both hesitation and the P0404 code.

Anonymous 2018-07-20 08:22

Also worth noting: the EGR position sensor has three wires — 5V reference, ground, and signal. If any of these wires are faulty or disconnected, it can interfere with the signal sent to the PCM. Without checking EGR data PIDs to see what the PCM is actually receiving, troubleshooting remains difficult. Manual circuit checks may help identify wiring issues.

Anonymous 2018-07-20 08:39

Could you please send instructions on how to perform these diagnostics? My email is Tbroecker01@gmail.com.