P0172

DTC P0172 System Too Rich (Bank 1, Sensor 1) (Part 1 Of 2):

DTC P0172 System Too Rich (Bank 1, Sensor 1) (Part 2 Of 2):

Heated Oxygen Sensor (HO2S 1) (Bank 1, Sensor 1):

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 Vehicle Control Module-A (VCM-A) monitors the oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with the Tech 1. Ideal fuel trim values are around 128; if the oxygen sensor signal is indicating a lean condition the VCM-A will add fuel, resulting in fuel trim values above 128. if a rich condition is detected, the fuel trim values will be below 128, indicating that the VCM-A is reducing the amount of fuel delivered. If an excessively rich condition is detected, the VCM-A will set DTC P0172. DTC P0172 is a type "B" DTC.

DTC PO172 WILL SET WHEN
^ No Heated Oxygen Sensor (HO2S) DTCs.
^ No Manifold Absolute Pressure (MAP) DTCs.
^ No Exhaust Gas Recirculation (EGR) DTCs.
^ No Evaporative Emissions (EVAP) System DTCs.
^ No Engine Coolant Temperature (ECT) DTCs.
^ No Intake Air Temperature (IAT) DTCs.
^ No Vehicle Speed Sensor (VSS) DTCs.
^ Throttle position is less than 90%.
^ Engine speed is between 373 RPM and 4500 RPM.
^ Barometric Absolute Pressure (BARO) is greater than 70 kPa (21 Hg).
^ Engine Coolant Temperature (ECT) is between 0°C and 100°C (32°F and 212°F).
^ Manifold Absolute Pressure (MAP) is between 20 kPa and 99 kPa (6 Hg and 29 Hg).
^ Intake Air Temperature (IAT) is between -30°C (-22°F) and 70°C (158°F).
^ Vehicle speed is less than 83 mph.
^ The average short term fuel trim samples is no more than 115.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
When DTC P0172 has initially been set, a software flag indicating an emissions-related fault will be set for 3 trips, after which the flag will clear provided the rich condition is no longer present. However, if conditions for setting DTC P0172 are detected during a trip while the flag is still set, the VCM-A will turn "ON" the Malfunction Indicator Lamp (MIL) (Service Engine Soon). The MIL will remain "ON" for all subsequent trips until the DTC has been cleared by service or the rich condition has not been detected and conditions for checking fuel trim have been met for 3 consecutive trips.

DTC P0172 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

Important
^ To complete a trip cycle for the fuel trim diagnostic, test must be enabled and run according to the "DTC P0172 Will Set When" criteria above. A trip is not considered complete until the fuel trim diagnostic has been run by the VCM-A.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Visually/physically checking items which may cause a rich condition may determine the cause of DTC P0172 being set.
2. Checks fuel system for problems.
3. Silicon contamination of the Heated Oxygen Sensor (HO2S 1) can cause a false rich indication to be seen by the VCM-A, The VCM-A will then reduce the amount of fuel delivered, possibly causing severe driveability symptoms.

DIAGNOSTIC AIDS
If the problem cannot be isolated using the diagnostic charts, try monitoring Long Term (L.T.) fuel trim and fuel trim cell while operating the vehicle under various loads. This may isolate the condition which caused PO172 to be set.

A condition that causes DTC P0300 "Random Misfire Detected" may also set DTC P0172; conversely, an extremely rich condition which sets DTC P0172 can cause a misfire at idle and DTC P0300 to set. If the cause of DTC P0172 cannot be determined and DTC P0300 is also set, refer to DTC P0300 Random Misfire Detected. P0300