P0400 -- Is it Normal when ...

[crosis]

My 1998 Nissan Quest is showing the "Service Engine Soon" light. I did an OBD II diagnostic and it reported P0400.

I have a vacuum pump and so tested the EGR Valve by applying a vacuum to the valve while the car was idle. The vehicle started to rumble so the EGR valve looked good. I then jacked up the car, put it in D, then revved it to between 2000 to 4000 rpm while the vacuum hose from the EGR Back Pressure Transducer (BPT) Valve to the EGR valve was disconnected. I tried to feel for any vacuum in the hose coming from the EGR BPT Valve but felt no vacuum -- i only kept capping and uncapping the hose end with my finger but felt no pressure difference.

My understanding is there should be some vacuum coming from the EGR BPT Valve when in D and revving between 2000 to 4000 rpm but if i did it correctly i feel no vacuum pressure from the hose line. How do you suggest i proceed in diagnosing this P0400 issue?

Thanks

[centralcoaster33]

Does your vacuum pump have a dial to measure with? I'd use that instead of my finger to measure vacuum...

Anyway, for code P0400, look to the FSM. As of right now, I'm not getting through with the link for your year, so I'm looking at the FSM for a 1997 Quest. Here's a link to that EC chapter, check out page EC-163 for diagnoses procedures... On my 240sx, it was the purge control solenoid valve that went bad. I pulled one at the junk yard for cheap. That was after doing all the vacuum testing and running power to the solenoid to listen for clicking open and closed. Actually, this very issue is the reason for me owning a vacuum pump thing now.

http://www.nicoclub.com/service-manual? ... 7_Quest/ec