Troubleshooting P0172 DTC [Archive] - Forum


View Full Version : Troubleshooting P0172 DTC

JHawk GT
07-25-2004, 09:56 AM
Since the weather turned warmer this spring (May), Iíve been getting the P0172 (bank 1 rich) code. The only mods Iíve done have been Dr. Speed CAI, Pro-M maf sensor, and Borla catback. All these mods were done within a week of each other in late Jan with no problems until May.

Iíve had more time to log some data over the past few days and long term fuel trim has ranged from Ė5 to Ė28. The third step in the diagnostic process from gmís service manual is to watch the voltage of the precat O2 sensor. The specified range is 200-800mV at idle. Does that mean that no values outside this range should be observed? My voltages go all the way down to 30mV. I regularly see values below 200mV and have seen a few above 800mV. Another interesting observation is that my engine is in closed loop from a cold start. The only tests that have failed have been the O2 sensor lean to rich and rich to lean switches. A/F ratio is 14.7. All connections (IAT, etc) have been checked and rechecked and Iím positive that I didnít mess with any of the O2 sensor connections during mod install.

Does anyone have any logged data from the precat O2 sensor showing voltages outside of 200-800mV at idle? I know a few members here have the car-code scan tool and thatís what Iíve been using. I was worried that my Pro-M meter was miscalibrated since they didnít send me a cal sheet, but if that was causing a problem, wouldnít I have had a problem from day one, i.e. lean not rich? Iím thinking itís the precat O2 sensor, but itís strange that it would go out so soon.

Help :confused:

JHawk GT
07-27-2004, 11:30 AM
No one has any ideas or info?????

07-27-2004, 05:30 PM
i am sorry. mine did that when i was trying to top( on a track. took it to gm they could not find anything wrong it. maybe was cutting fuel off for some reason. that i can not explain. it only comes on when you get on it !!!

07-27-2004, 05:32 PM
If this helps... I believe that code comes around when your MAF is not calibrated correctly for the type of intake.. Slim25 / Craig99SE had similar problems IIRC. I'd tell you to search it out but the search index won't be repaired for a few hours.. You can try later tonight and it should work.

JHawk GT
07-27-2004, 08:31 PM
Thanks, Iceman. I guess I'll have to keep looking for the problem. This thread ( was what led me to ask about running rich. Apparently there were no non-CAI meters calibrated by Pro-M for our engines as of 12/03 and I purchased mine in Nov. Also, Tom mentioned that if it were not calibrated for cold air, lean fuel trim would result. I also saw that GTSpeed had the same problem with the same setup, but it went away.

It's still puzzling that I this problem didn't start until months after install...

06-07-2009, 07:16 PM
Bringing this thread back. Will the P0172 code go away with time? New stock MAF installed.......just keeps coming runs great thought, the SES just wont go away

06-08-2009, 08:34 AM

06-12-2009, 08:15 PM