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1997 Nissan Quest GXE with P0400 and P0325: Causes, Fixes, and Smog Check Implications

Model: 1997 Nissan Quest GXE Fault Code: P0325 Posted: 2011-01-07 13:51

I own a 1997 Nissan Quest GXE with a 3.0L V6 engine and approximately 174,900 miles. Two weeks ago, my mechanic replaced the front exhaust manifold due to a crack and also repaired the rear manifold studs near the firewall. After the repair, the vehicle ran normally, but three days later the check engine light illuminated. I took it to a service center off the highway where they diagnosed two trouble codes: P0400 (Exhaust Gas Recirculation Flow Malfunction) and P0325 (Knock Sensor Circuit Malfunction). The codes were cleared, and I drove an additional 140 miles without any issues. When I returned to town, I visited another service center for a recheck. They confirmed that P0325 was still present. I'm now wondering whether the exhaust manifold repair could have caused these codes or if they are unrelated. Should I continue driving the vehicle and wait for symptoms to return, or should I address the issue immediately? Is there a connection between the work done on the manifolds and the appearance of these diagnostic trouble codes? Additionally, I recently used a fuel system cleaner—typically added when the tank is 1/4 full before refilling—but this time I added it after filling the tank. The MIL lit up as the gauge approached empty. Could this have contributed to any EGR-related issues? I'm trying to rule out all possible causes.

Related fault codes

P0325P0400

Comments (7)

Anonymous 2011-01-07 17:58

P0325 is a common code in 1997 Nissan Quest GXE models and often does not trigger the Malfunction Indicator Lamp (MIL), especially on older V6 engines. As for P0400, it may be related to the recent exhaust manifold work—such as a disconnected or improperly installed component—or could simply be coincidental. I recommend returning to the original shop for a thorough inspection to ensure no components were overlooked during the repair.

Anonymous 2011-01-08 16:11

Thanks for the insight, Jeff. After some research, it does appear that P0325 is fairly common in this model and typically doesn't activate the MIL. I'm now focusing on whether P0400 returns. I’m also considering if my recent use of a fuel system additive—added after filling the tank instead of before—might have played a role, as the MIL lit up when the gauge approached empty.

Anonymous 2011-01-08 23:03

It's highly unlikely that a fuel additive used at an unusual timing would cause an EGR system malfunction. The EGR and fuel system operate independently, so such a connection is not technically plausible.

Anonymous 2011-01-08 23:15

Agreed—this seems improbable. I'm just trying to explore all possible factors. So far, the MIL has remained off. I plan to take the vehicle on several high-mileage drives over the next few days to test for recurrence.

Anonymous 2011-01-12 22:14

P0400 returned and triggered the MIL again—along with P0325. I'm now scheduling a diagnostic at a repair shop as soon as possible. My priority will be determining whether the issue stems from the EGR system or faulty wiring connections.

Anonymous 2011-01-13 06:00

If this vehicle uses the same 3.0L V6 engine found in some front-wheel-drive Fords, Mercury Villagers, and Nissan Quests, then a defective Diesel Particulate Filter (DPFE) or clogged throttle body ports could be potential causes—similar to issues seen in older Windstar models.

Anonymous 2011-01-19 14:43

I found a reputable shop offering a full P0400 diagnostic for $65 on walk-in basis. They discovered no vacuum signal to the EGR system. The root cause was identified: the back pressure transducer hose had been disconnected during the exhaust manifold repair and was never reconnected. I replaced it with a silicone hose, which cost an additional $5. This confirms that the previous shop likely either intentionally or accidentally disconnected the hose during maintenance—now resolved. P0400 is fixed. Regarding P0325 (knock sensor), I now need to decide whether to repair it. Possible issues include a faulty knock sensor or its wiring harness. However, I don’t need to fix this immediately because my next smog check is in December 2012. EDIT: I found a relevant discussion at http://forums.nicoclub.com/my-car-faile ... 42203.html. As a licensed California smog inspector, I can confirm that P0325 will not result in a failed OBDII inspection if the MIL is not illuminated and the system has completed monitoring. The law requires an active MIL command to trigger failure—without it, no penalty occurs. Therefore, P0325 poses no smog check risk. I may choose to repair it later for peace of mind, but it’s not a current necessity.