rich to lean and lean to rich
Thread Starter
Senior Member
Joined: 01-07-2016
Posts: 112
From: Ashland City, tn
rich to lean and lean to rich
This has been a common problem with my HHR LT 2010 2.2L with about 122,240 miles on it so far. Some times it has a P0172 (rich condition),CEL goes off and comes back on as a P0171 (lean condition). When car was at dealership for about a month with my gauge probelms (car was running lean for them). They did a smoke test for a vacuum leak and found none. They changed the purge valve and no charge ( CEL pointed them in that direction). Car runs fine and I still haven't checked the fuel pressure yet. We even used some brake cleaner to test for vacuum leak and found none. Any suggestions as to check or test next.
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Joined: 01-23-2009
Posts: 26,532
From: Fredericksburg,VA
search youtube for "fuel trim". There are several good vids about that so you can understand what it actually means.
I can try; basically the #1 O2 sensor tells the computer if the engine is running rich or lean. The computer then tries to adjust the A/F ratio to the perfect stoichiometry. Sometimes it compensates one way and the broken part forces the sensor the other way too far.
The #2 O2 sensors monitors the health of the catalyst using data from the #1 sensor, so that is not a suspect.
I would take a flying guess at a bad injector.
Having them cleaned and tested costs about the same as new ones. If you replace them be sure they are the identical part numbers.
They replaced the purge valve under the hood? Or the one by the gas tank?
I can try; basically the #1 O2 sensor tells the computer if the engine is running rich or lean. The computer then tries to adjust the A/F ratio to the perfect stoichiometry. Sometimes it compensates one way and the broken part forces the sensor the other way too far.
The #2 O2 sensors monitors the health of the catalyst using data from the #1 sensor, so that is not a suspect.
I would take a flying guess at a bad injector.
Having them cleaned and tested costs about the same as new ones. If you replace them be sure they are the identical part numbers.
They replaced the purge valve under the hood? Or the one by the gas tank?
Administrator
Joined: 10-13-2011
Posts: 40,083
From: Welland,Ont Canada
Per P0172
http://www.obd-codes.com/p0172
I'm more inclined to the leak aspect, as in flex joint in the exhaust leak!
http://www.obd-codes.com/p0172
I'm more inclined to the leak aspect, as in flex joint in the exhaust leak!