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 differently during Open and Closed Loop. During Open Loop, the PCM 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 PCM to calculate short and long term fuel trim, delivery adjustments. If the O2S sensors indicate a lean condition, the fuel trim values will be above 0 percent. If the O2S sensors indicate a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the heated oxygen sensors (HO2S) voltage signals. The long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. The 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 DTC will set. If the PCM detects excessive vapor then a pass is logged.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0107, P0108, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0122, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0401, P0403, P0404, P0405, P0410, P0412, P0418, P0440, P0442, P0446, P0506, P0507, P1404, or P1441 are not set.
^ The engine coolant temperature (ECT) is between 20-110°C (68-230°F).
^ The intake air temperature (IAT) is between 18-70°C (64-158°F).
^ The manifold absolute pressure (MAP) is between 15-105 kPa (2.1-15.2 psi).
^ The vehicle speed is less than 132 km/h (82 mph).
^ The engine speed is between 550-4,000 RPM.
^ The barometric pressure (BARO) is more than 70 kPa (10.1 psi).
^ The mass airflow (MAF) is between 2.8-150 g/s.
^ The fuel level is more than 10 percent.

CONDITIONS FOR SETTING THE DTC
^ The average long term fuel trim value is below 13 percent.
^ All of the above conditions are present for 40 seconds.

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 effect the fuel trim.
^ A bad MAF sensor can cause a rich condition and set this DTC. Refer to DTC P0101. P0101
^ Use a scan tool in order to review Failure Records. If an intermittent condition is suspected, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-6:

Steps 7-8:

The numbers below refer to the step numbers on the diagnostic table.
5. If no condition was found, refer to Fuel System Diagnosis for possible fuel condition. Component Tests and General Diagnostics
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 no conditions are found, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be at fault.