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 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). If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. Short Term fuel trim values change rapidly in response to the HO2S voltage signals. 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 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-P0206, P0300, P0401, P0403, P0404, P0405, P0410, P0412, P0418, P044, P0442, P0446, P0506, P0507, P1404 and P1441 are not set.
^ The Engine Coolant Temperature (ECT) is between 20°C (68°F) and 110°C (239°F).
^ The intake air temperature is between 18°C (0°F) and 70°C (158°F).
^ The Manifold Absolute Pressure (MAP) is between 15 kPa (2.1 psi) and 105 kPa (15.2 psi).
^ The vehicle speed is less than 132 km/h (82 mph).
^ The engine speed is between 600 and 4000 RPM.
^ The barometric pressure is more than 70 kPa (10.1 psi).
^ The Mass Airflow (MAF) is between 5.0 g/s and 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
^ First failure:
- The MIL is not turned ON.
- A DTC is stored in memory under Failed Last Test.
- The Failure Records are stored.
^ Second consecutive drive cycle with a failure:
- The MIL is turned ON.
- A DTC is stored in memory under history.
- The Freeze Frame data is stored.
- The Failure Records are stored.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after the third consecutive trip the diagnostic has run and passed.
^ The history DTC will clear if the fault conditions have not been detected for 40 warm-up cycles.
^ A scan tool can be used to clear DTC information.

DIAGNOSTIC AIDS
Fuel contamination, such as water and alcohol will effect fuel trim.
^ A malfunctioning mass air flow sensor can cause a rich condition and set this DTC. Refer to DTC P0101. P0101
^ Using scan tool, review Failure Records. If intermittent condition is suspected, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-8:

The numbers below refer to the step numbers on the diagnostic table.
5. If conditions were not corrected, refer to Fuel System Diagnostic for possible fuel problem. 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 leaking regulator. If conditions were not corrected, a worn cam, worn intake or exhaust valves or other engine mechanical failure may be at fault.