Code P0172: Fuel Trim Rich: Notes
A closed loop air/fuel metering system is used to provide best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. Scan tester monitors fuel trim values, and will indicate a change made to fuel delivery by long and short term fuel trim values.
Ideal fuel trim values are about 128. If oxygen sensor signal indicates a lean condition, PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating PCM is reducing amount of fuel delivered. PCM will set Code P0172 if an excessively rich condition is detected. Code P0172 will set when the following conditions are present.
- Codes P0101, P0117, P0118, P0122, P0123, P0501 and P0502 are not set.
- Engine coolant temperature is between 176°F (80°C) and 230°F (110°C).
- Steady throttle less than 91 percent.
- Vehicle speed is less than 70 MPH.
- On VIN L, engine RPM is 1000-4000 RPM, or on VIN 1, engine RPM is 0-4000 RPM.
- EVAP canister purge duty cycle is less than 80 percent.
- Long term fuel trim is less than 100.
- Short term fuel trim is less than 94.
- All conditions exist for more than 25 seconds.
Preliminary Inspection
- Ensure air intake duct is not collapsed or restricted and air filter is not plugged.
- Check for damaged or partially plugged throttle body inlet screen.
- Check for proper operation of IAC system.
- Check fuel pressure regulator operation, ensuring diaphragm is not ruptured.
- Check for proper operation and mounting of throttle position sensor.NOTE: To complete a trip cycle for fuel trim diagnostic, fuel trim diagnostic test must be enabled and run according to conditions required to set Code P0172. A trip is not considered complete until fuel trim diagnostic has been run by PCM.NOTE: Test numbers refer to numbers on diagnostic chart.
- Visually/physically checking components/systems which may cause a rich condition may determine cause of Code P0172.
- MAF sensor which causes PCM to read a higher then actual airflow can cause a rich condition, and Code P0172 to set.
- Silicone contamination of Heated Oxygen Sensor (HO2S) can cause a false rich indication that will be sensed by PCM. PCM will then reduce amount of fuel delivered, possibly causing severe driveability symptoms.