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 FT values are around 0 percent; if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in FT values above 0 percent. If a rich condition is detected, the FT 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 PCMs maximum authority to control Long Term FT allows a range between approximately -25 percent and +20 percent. The PCM monitors FT under various operating conditions (fuel trim cells) before determining the status of the fuel trim diagnostic. The fuel trim cells are weighted (assigned a percentage of importance in determining total fuel trim status for the diagnostic) as follows:
^ Idle, purge commanded (Cell 0 - approximately 10 percent)
^ Deceleration, purge commanded (Cell 1- approximately 15 percent)
^ Normal driving, purge commanded (Cell 2- approximately 25 percent)
^ Normal driving, no purge commanded (Cell 6- approximately 45 percent)
^ Idle, no purge commanded (Cell 9- approximately 5 percent)

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 more 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 approximately -25 percent.
^ Short Term FT is at or near maximum authority of approximately -25 percent.
^ All conditions have been met in FT Cells 1, 2, 6, 9 and/or 0.

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
Check 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). Component Tests and General Diagnostics Component Tests and General Diagnostics
^ EVAP canister - Check the EVAP canister for fuel saturation. If the canister is full of fuel, visually and physically check the EVAP and fuel system components for damage.
Refer to EVAP Control System Diagnosis. Component Tests and General Diagnostics
^ Mass air flow sensor - Disconnect the MAF sensor and see if rich condition is corrected. If so, replace the MAF sensor.
^ Fuel pressure regulator - Check for a leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for the presence of fuel. If a problem is found, replace the fuel pressure regulator.
^ 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, check the TP sensor for loose mounting screws. If the TP mounting screws are OK, replace the TP sensor.
^ Poor connection at the PCM - Inspect harness connectors for the following conditions.
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection
^ Damaged harness - Inspect the wiring harness for damage.
^ If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving connectors and wiring harnesses related to the engine harness. A change in the display will indicate the location of the malfunction.

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent and Poor Connections in Diagrams.

TEST DESCRIPTION
The 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.