P0172 error code on a 2003 GMC Envoy


Old 10-28-11, 11:30 AM
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P0172 error code on a 2003 GMC Envoy

I am looking for suggestions as too a fuel mixture too rich code. I read that it could be a faulty fuel pressure regulator or fuel injectors. I have been told that it is probably the upstream oxygen sensor but either way I would rather not spend a month's pay to have the vehicle "what-ifd" at a shop if I can narrow it down some myself. Any thoughts/suggestions would be greatly appreciated.

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Old 10-28-11, 05:56 PM
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I would start by cleaning or replacing the Mass Air Flow Sensor. If it is not working properly it can tell the computer the engine is getting more oxygen than it is and it will over compensate the amount coming out of the fuel injectors.

If that doesn't clear things up, another possible cause is a coolant temperature sensor that could also send false information in regards to a cold engine condition which again leads to over compensating with the amount from the injectors. I think that a faulty 02 sensor is most likely not involved as it should then fail the computer readiness check and throw a different code of it's own in, at least probably most cases.
Old 11-08-11, 09:17 AM
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Don't clean the Mass Air Flow Sensor if you do that you will have more troubles setting other DTC's and have to replace it anyhow. First check for kinks in any vacuum lines or any restriction of air flow going to your throttle body. I don't know what scan tool you are using so if you can scan and check the fuel trim index it should be at -35%. If yes then go and check the O2 Sensors parameters which should be 200-800mV..if not then replace the O2 sensor and it should solve your problem.
Old 11-10-11, 12:02 AM
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A code P0172 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters can cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak.
There could be a fuel pressure or delivery problem
Possible Solutions

Possible solutions include:

Inspect all vacuum and PCV hoses, replace if necessary
Cleanthe MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect fuel lines for cracks, leaks, or pinches
Check the fuel pressure at the fuel rail
Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)
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