P0172

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

CIRCUIT DESCRIPTION
To provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air/fuel metering system is used. While in closed loop, the PCM monitors the HO2S 1 signal and adjusts fuel delivery based upon the HO2S signal voltage. A change made to fuel delivery will be indicated by the long and Short Term FT values which can be monitored with a scan tool. Ideal fuel trim values are around 0 percent; if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in fuel trim values above 0 percent. If a rich condition is detected, the fuel trim values will be below 0 percent, indicating that the PCM is reducing the amount of fuel delivered. If an excessively rich condition is detected, DTC P0172 will set.

The PCM's maximum authority to control Long Term FT allows a range between -23 percent and +16 percent. The PCM's maximum authority to control Short Term FT allows a range between -11 percent and +20 percent. The PCM monitors fuel trim under various operating conditions (fuel trim cells) before determining the status of the fuel trim diagnostic. The fuel trim cells used to determine fuel trim are as follows:
^ Idle, purge commanded.
^ Deceleration, purge commanded.
^ Normal driving, purge commanded.
^ Normal driving, no purge commanded.
^ Idle, no purge commanded.

The vehicle may have to be operated in all of the above conditions before the PCM determines fuel trim status. The amount that fuel trim deviates from 0 percent in each cell and the amount that each cell is weighted directly affects whether or not the vehicle must be operated in all of the cells described above to complete the diagnostic.

CONDITIONS FOR RUNNING THE DTC
^ No VSS, TP sensor, EVAP system, HO2S, Misfire, IAT sensor, MAP sensor, Idle speed, Fuel Injectors, IC/Bypass, EGR Pintle, EGR Flow, ECT sensor CKP sensor CMP sensor, or MAF sensor DTCs set.
^ Engine coolant temperature between 20°C (68°F) and 110°C (230°F).
^ Intake air temperature is between -18°C (0°F) and 70°C (158°F).
^ BARO is greater than 70 kPa.
^ Manifold absolute pressure is between 15 kPa and 85 kPa.
^ Throttle angle is less than 90 percent.
^ Vehicle speed is less than 82 mph.
^ Mass air flow is between 3 g/s and 150 g/s.
^ Engine speed between 600 and 4000 RPM.

CONDITIONS FOR SETTING THE DTC
^ Long Term FT is at or near maximum authority of -23 percent.
^ Short Term FT is at or near maximum authority of -11 percent.
^ All conditions have been met in Fuel Trim Cells 1, 2,6, 9 and/or 10.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
^ If the misfire is determined to be catalyst damaging, the PCM will flash the MIL.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Inspect the following items:
^ Fuel injectors: Refer to Fuel Injector Coil Test Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F).
^ EVAP Canister: Inspect the EVAP canister for fuel saturation. If the canister is full of fuel, visually and physically inspect the EVAP and fuel system components for damage.
Refer to Idle Air Control System Diagnosis.
^ Mass Air Flow Sensor: Disconnect the MAF sensor and see if rich condition is corrected. If so, replace the MAF sensor. Refer to MAF Sensor Replacement.
^ Fuel Pressure Regulator: Inspect for a leaking fuel pressure regulator diaphragm by Inspecting vacuum line to regulator for the presence of fuel. If a problem is found, replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement.
^ TP Sensor: An intermittent TP sensor output will cause the system to go rich due to a false indication of the engine accelerating. Throttle Angle displayed on a scan tool should increase steadily from 0 percent to 100 percent when opening the throttle. If not, inspect the TP sensor for loose mounting screws. If the TP mounting screws are OK, replace the TP sensor. Refer to TP Sensor Replacement.

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Diagrams for diagnosis and repair.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Diagrams for diagnosis and repair.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION
Numbers below refer to the step numbers on the Diagnostic Table.
2. DTCs other than P0172 may indicate a condition present which may cause a rich condition. If this is the case, repairing the condition which caused the other DTC will most likely correct the DTC P0172.
4. If the DTC P0172 test passes while the Fail Records conditions are being duplicated, the rich condition is intermittent. Refer to Diagnostic Aids for additional information on diagnosing intermittent conditions.