P0172
DTC P0172
CIRCUIT DESCRIPTION
The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop the ECM determines fuel delivery based on sensor signals without oxygen sensor (O2S) input. During Closed Loop, the oxygen sensor inputs are added and used by the ECM to calculate short and long term fuel trim (FT) fuel delivery adjustments. If the O2S indicates a lean condition, the FT values will be above 0 percent. If the O2S indicates a rich condition, the FT values will be below 0 percent. Short term FT values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. The FT diagnostic will conduct a test to determine if a rich failure actually exists, or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition. If the ECM detects an excessively rich condition, DTC P0172 or P0175 sets.
DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC P0172 Fuel Trim System Rich Bank 1
- DTC P0175 Fuel Trim System Rich Bank 2
CONDITIONS FOR RUNNING THE DTC
- DTCs P0030-P0032, P0036, P0038, P0050-P0052, P0056-P0058, P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131-P0135, P0137-P0141, P0151-P0155, P0157-P0161, P0221, P0222, P0223, P0300, P0301-P0308, P0335, P0340, P0341, P0345, P0346, P0365, P0366, P0390, P0391, P0443, P0446, P0458, P0459, P1111, P1112, P1114, P1115, P1137, P1138, P1157, P1158, P1380, P1381, P2135, P2231, 2234 are not set.
- Closed Loop is active.
- The engine coolant temperature (ECT) is more than 70°C (158°F).
- The intake air temperature (IAT) is more than -7°C (+19.4°F).
- The vehicle speed is less than 137 km/h (85 mph).
- The engine speed is more than 500 RPM.
- The barometric pressure (BARO) is more than 740 kPa (107.3 psi).
- The mass air flow (MAF) is more than 60 mgstk.
- The fuel level is more than 9.8 percent.
- DTC P0172 and P0175 run continuously when the above conditions have been met.
CONDITIONS FOR SETTING THE DTC
- The combined value of the Short Term FT and the Long Term FT parameters are less than -25 percent.
- The above condition is present for more than 3 minutes.
ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.
DIAGNOSTIC AIDS
- Fuel contamination, such as water or alcohol will effect FT.
- A malfunctioning MAF sensor can cause a rich condition and set this DTC. Refer to DTC P0101. P0101
- An evaporative emission (EVAP) canister that is saturated will cause a rich condition. If the conditions were not corrected, a worn cam shaft, worn intake valves, worn exhaust valves, or other engine mechanical failure may be the problem.
- Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions. Intermittent Conditions
TEST
