P0172

DTC P0172 Fuel Trim System Rich

System Description
In order to provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air and fuel metering system is used. While in a closed loop, the PCM monitors the oxygen sensor signal voltage. The PCM adjusts fuel delivery based on signal voltage. The Long and Short Term FT values will indicate a change made to the fuel delivery. The ideal FT values are around 128 (0 percent). Whenever the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in FT values above 128 (0 to 100 percent). Whenever a rich condition is detected, the FT values will read below 128 (0 to -100 percent), indicating that the PCM is reducing the amount of fuel delivered. Whenever the exhaust emissions reach an excessive level due to a rich condition, a FT DTC will set.

Conditions for Running the DTC
- No active MAP DTCs
- No active IAT DTCs
- No active ECT DTCs
- No active TP DTCs
- No active oxygen sensor DTCs
- No active injector control DTCs
- No active misfire DTCs
- No active knock sensor DTCs
- No active CKP DTCs
- No active CMP DTCs
- No active EVAP DTCs
- No active VSS DTCs
- No active IAC DTCs
- No active PCM memory DTCs
- Intake air temperature (IAT) is between -25° C (-13° F) and 115° C (175° F)
- Engine coolant temperature is between 60° C (140° F) and 115° C (239° F)
- Engine speed is between 850 RPM and 3400 RPM
- Vehicle speed is below 82 mph (132 kph)
- MAP is above 26 kPa
- BARO is more than 72 kPa
- The fuel level is more than 10 percent

Conditions for Setting the DTC
- Fuel trim index is below 75 (-40 percent).
- Above conditions present for over 16 seconds.

Action Taken When the DTC Sets
- The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
- The control module will set the DTC and records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC
- The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
- A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22° C (40° F) from the startup coolant temperature and the engine coolant temperature is more than 70° C (158° F) during the same ignition cycle).
- Use the scan tool Clear Information function.

Diagnostic Aids
- Check for a 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

Check for a damaged harness. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving the connectors and wiring harness related to the engine harness. A change in the display will indicate the location of the fault.

Step 1:

Steps 2 - 3:

Step 4:

Steps 5 - 8:

Steps 9 - 12:

Steps 13 - 14:

Test Description
The numbers below refer to the step numbers on the diagnostic table:
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
2. A more negative value indicates the PCM is leaning the fuel mixture (rich condition) and a more positive value indicates the PCM is richening the fuel mixture (lean condition).
4. This step checks for a fuel delivery concern.