P0172

CIRCUIT DESCRIPTION
The powertrain control module (PCM) 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 during Open and Closed Loop. During Open Loop the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the PCM to calculate short and long term fuel trim, fuel delivery adjustments. Short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. The fuel trim index is the average of short and long term fuel trim and purge learn memory based on engine speed and load. Fuel trim 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 PCM detects an excessively rich condition, this diagnostic trouble code (DTC) will set. If the PCM detects excessive vapor then a pass is logged.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0201-P0204, P0300, P0301-P0304, P0325, P0341, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, or P1441 are not set.
^ The engine coolant temperature (ECT) is 60-115°C (140-239°F).
^ The intake air temperature (IAT) is -25 to +115°C (-13 to +239°F).
^ The manifold absolute pressure (MAP) is above 28 kPa (4.0 psi).
^ The vehicle speed is less than 132 km/h (82 mph).
^ The engine speed is between 550-3,600 RPM.
^ The barometric pressure (BARO) is more than 72 kPa (10.3 psi).
^ The fuel ethanol composition is less than 88 percent.
^ The fuel level is more than 9.8 percent.

CONDITIONS FOR SETTING THE DTC
^ The fuel trim index is below -46 percent.
^ The diagnostics have determined that a rich condition was not due to excessive vapor.

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 and alcohol, will affect the fuel trim.
^ The system will go rich if the injectors are supplying too much fuel.
^ Review the Failure Records with a scan tool. If intermittent condition is suspected, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-6:

Steps 7-8:

The number below refers to the step number on the diagnostic table.
6. An EVAP canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a bad regulator. If conditions were not corrected, a worn cam, worn intake or exhaust valves or other engine mechanical failure may be at fault.