Nissan Frontier Vibrates Going Uphill P0400

2003 Nissan Frontier with a 4cyl engine, just over 300k.

It vibrates and starts chugging anytime it’s under a small load, like going up a hill. Cruises nice and smooth on level ground or going downhill. Feels like a misfire, but idles perfectly and had new plugs/wires installed a few month ago with no problems.

So there’s no service engine light, and no codes set, but when I plug my scanner into it the code P0400 appears and disappears randomly on the screen but never sets itself in the computer.

My question is, where is a good starting point? Any components known to go bad in the EGR system? And would a bad/stuck EGR valve cause these symptoms?


PS - there is also a code set for the catalytic converter, it was catalyst efficiency below threshold but I don’t remember the exact code. Any way this could be part of the problem, or related in any way?

It could be that with an EGR fault the ECM is trying to retard the timing due to a looming pre-ignition rattle and that is the cause of the misfire or surge.

Given the 300k miles on the truck, a compression test should be done to make absolutely certain that you’re dealing with a good engine. A dropping cylinder could cause a problem like this also.


If your cat is plugged, your engine can’t breathe properly and you’ll have lousy power

Just something to consider

Thank you, I’ll keep both of those in mind as I’m working on the truck.