P0172

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 Powertrain Control Module (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 fuel trim values are around 128 (0 percent). Whenever the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128 (0 to 100 percent). Whenever a rich condition is detected, the fuel trim 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 fuel trim DTC will set.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0325, P0335, P0341, P0342, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, and P1441 are not set.
^ The Intake Air Temperature (IAT) is between -25°C (-13°F) and 115°C (175°F).
^ The Engine Coolant Temperature (ECT) is between 60°C (140°F) and 115°C (239°F).
^ Engine speed is between 550 RPM and 3600 RPM.
^ Vehicle speed is below 82 mph.
^ MAP is above 26 kPa.
^ BARO is more than 72 kPa.
^ Fuel ethanol composition less than 88 percent.
^ Fuel level is more than 9.8 percent.

CONDITIONS FOR SETTING THE DTC
The fuel trim index is below 65.

ACTION TAKEN WHEN THE DTC SETS
^ The Malfunction Indicator Lamp (MIL) illuminates if the fault is active within the same conditions for 2 out of 80 ignition cycles.
OR
^ The MIL will illuminates after two consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information.
^ A history DTC is stored.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the Freeze Frame conditions that the DTC failed.
^ A history DTC will clear after 40 consecutive warm up cycles without a fault.
^ A scan tool can clear the DTCs.

DIAGNOSTIC AIDS
^ Inspect 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.

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

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.