P0172 Fuel System Rich
Possible Causes Setting Conditions
Base engine "mechanical" fault affecting one or more cylinders
EVAP system component has failed or canister fuel saturated
Fuel control sensor is out of calibration (i.e., ECT, IAT or MAP)
Fuel system supplying too much fuel at idle speed or at cruise
Fuel injector(s) is leaking or stuck partially open (one or more)
HO2S is contaminated, deteriorated or it has failed
The Service Engine Soon (SES) lamp is on, Powertrain Control Module (PCM) code: P0172. The vehicle runs well, but fails emission test due to lamp on. The short term fuel trim value is -15% at idle. The long term fuel trim is near 0% at idle. Both values are near 0% at 3000. The ECT and IAT check normal. The MAP is 1.6v at idle, higher than expected.
1. Check the fuel pressure regulator, look for leak at the hose.
2. Check short term fuel trim and long term fuel trim values at idle and 3000 RPM.
3. The system is determined to be rich if the trim values stay below -10%.
4. Check the Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) values in scan data, check for accuracy.
5. Verify Manifold Absolute Pressure (MAP) sensor volts at idle, should be near 1.0-1.2 volts.
6. Run injector cleaner through the fuel rail.
7. Check short term fuel trim and long term fuel trim values again with the canister purge disabled.
8. Check engine oil condition.
9. Verify Exhaust Gas Recirculation (EGR) actual % at idle, should be 0%.
10. Clean the throttle body.
11. Clean the fuel injectors.
2000 S10 2.2
The engine is running rich setting code P0172, fuel pressure is running 100 PSI all the time.
1. Check for a blockage or restriction in the return line back to the fuel tank from the fuel filter.
2. If the fuel lines are OK, then try a new fuel filter.
This fuel filter is also the fuel pressure regulator for the system. Normal pressure for this vehicle is 55-60 PS
On my VIN 5 S-10 2.2L I had the same code. No PCV valve and no external fuel pressure regulator. The scanner showed both Short and long term fuel trims fixed at -16% and O2 sensor voltage at 1.00V, The ECT read 199°F. I removed a vacuum hose and the readings Dropped to -3% STFT, and O2 was fluctuating .29V up to .890V. I did not check the fuel pressure.
Long story short I replaced the fuel filter: STFT at idle fluctuates 3% to -3%, LTFT dropped to -3%, the O2 sensor is very active.
I will check the fuel filter and post the result.