Po172 is not always an indication of a rich condition. the following diagnostic aids will help you get an idea on what it could be. You need a scan tool that can read voltage data from the o2 sensor to determine if their faulty.
DIAGNOSTIC AIDS DTC P0172 indicates the engine is running rich. The following are possible causes of a rich air/fuel mixture:
To verify the system is running rich, use Scan tool to monitor HO2S-1 and HO2S-2. If both sensors are above 600 mV , the system is running rich and the oxygen sensors are probably not at fault.
No this code has nothing to do with the transmission, usually when you clear it it does not come back right away.
If you read o2 sensor voltage with your scanner and they read above 600mv then the system is running rich and the o2 sensor are not the problem, then you look for a vacuum leak, exhaust leak. if you find none then one of the injectors may be leaking.
If the HO2S-1 AND 2 read below 600mv then they would be the faulty part.
how can you tell if one of the injectors is leaking I will try that on reading the oxygen sensor voltages though and see what they read first
Well. the easy way but not real efficient is if the O2 sensors are reading within the specs, and there are no vacuum or exhaust leaks. and code po172 is present that's an indication of a rich condition.
there are two ways to test the injectors,
1. to remove them out of the intake and place a dry paper under them for a while
then if part of the paper becomes wet under an injector then that injector is leaking.
2. You can do an injector balance test using a good scan tool.
bank 1 sensor
rich-lean thres volt 0.555 volts
lean - rich thres volt 0.530 volts
low voltage switch line 0.350 volts
high voltage switch time 0.650 volts
rich lean switch time 0.032 volts
lean rich switch time 0.024
If those are active readings of the senor then the senor is not reading within specs
if there are no exhaust leaks around the senor then replace the senor.