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#4461764 - 07/17/17 12:46 PM EGR code (P0401) 2002 Isuzu Trooper (CA smog fail)
zanzabar Offline

Registered: 06/21/09
Posts: 424
Loc: NorCal
Isuzu Trooper 2002, ~100,000 miles. In good shape, runs and idles normally - idles a bit high though(~1000rpm?). I've been fighting an EGR insufficient flow code forever. Replaced EGR, cleaned input and output tubes thoroughly, cleaned TB thoroughly, removed and cleaned intake plenum THOROUGHLY. Still comes back intermittently. Replaced intake manifold gaskets. Also has several other intermittent codes that stay off for awhile and comeback occasionally then go away again: P0420 (catalyst/O2), P0446 (EVAP). Those two codes have been occasional problems for years, but we've always been able to clear them long enough to pass the smog test. Not this time though. It's the P0401 that is driving me nuts, but perhaps these are all related and I'm not aware of something that needs to be done that'll fix all three. O2 sensors are fairly new (~20k miles ago). Perhaps it's just that the cat has to be replaced? Suggestions on where to go next would be appreciated!
2007 Volvo V70 (142k miles)
2014 Ford Focus (31k miles)

#4461933 - 07/17/17 02:48 PM Re: EGR code (P0401) 2002 Isuzu Trooper (CA smog fail) [Re: zanzabar]
DerbyDave Offline

Registered: 10/27/15
Posts: 218
Loc: KS
I don't know about the Isuzu but some older fords have a DPFE sensor that is prone to failure that causes a P0401 to be set
1997 Ford Taurus
2007 Honda Ridgeline
2003 Suzuki GZ250
1986 Suzuki Cavalcade
2014 Nissan LEAF (Gone)

#4461950 - 07/17/17 03:19 PM Re: EGR code (P0401) 2002 Isuzu Trooper (CA smog fail) [Re: zanzabar]
zanzabar Offline

Registered: 06/21/09
Posts: 424
Loc: NorCal
I don't think it has one of those.
2007 Volvo V70 (142k miles)
2014 Ford Focus (31k miles)

#4461955 - 07/17/17 03:26 PM Re: EGR code (P0401) 2002 Isuzu Trooper (CA smog fail) [Re: zanzabar]
supton Offline

Registered: 11/09/08
Posts: 11920
Loc: NH
EGR insufficient flow, how would that be triggered? I'd think the MAF would see less air through it; or the O2 sensor would lean out. Or both. An air leak after the MAF would make the MAF read low and lean out the exhaust. Not sure what an exhaust leak would do. So I'm not sure how a leak would come into play, but am wondering if it's somehow in the piping, an exhaust leak of some sort.

Just trying to figure out how it knows there is an EGR problem, as that might indicate where to look.

Three dissimilar codes though could point to a grounding problem, or other wiring issue.
2011 Toyota Camry, base, 2.5L/6MT, 160k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 143k, ours
1999 Toyota Camry LE, 2.2L/4AT, 181k, his

#4462032 - 07/17/17 04:35 PM Re: EGR code (P0401) 2002 Isuzu Trooper (CA smog fail) [Re: zanzabar]
FlyNavyP3 Offline

Registered: 07/04/16
Posts: 1407
Loc: Jacksonville, FL
Does it measure EGR temperature to determine flow?
P-3C and P-8A Maritime Weapons and Tactics Instructor, Instructor Tactical Coordinator and Mission Commander

#4462036 - 07/17/17 04:39 PM Re: EGR code (P0401) 2002 Isuzu Trooper (CA smog fail) [Re: zanzabar]
Oro_O Offline

Registered: 09/20/14
Posts: 1351
Loc: Seattle-ish, WA
I have a similar (Acura SLX) and had the evap code plague me a while. It was a chronically disconnecting breather tube under the engine cover. Check your hoses are all good and not leaking - dry rotted but otherwise look ok, etc. I think that can make the 401 and 446, and then the 420 follows from those.

On a side note, if your oil consumption is still moderate, be sure to use a VERY high quality oil at moderate OCIs. These have the same oil drain back/oil control ring issue that plagues Saturns, some Mazdas, and some Toyota I4s. I understand some very late 2002 models finally had the fix incorporated (more drain holes drilled under rings and in piston skirts), but most did not.

Also ask at in either the General or "drivetrain problems" section. More specific knowledge is there.