P0171

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 the Short Term FT values will indicate a change made to the fuel delivery system. The ideal FT values are around 0 percent. Whenever the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in FT values from 0 to +100 percent. Whenever the exhaust emissions reach an excessive level due to a lean condition, DTC P0171 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 3,400 RPM
- Vehicle speed is below 82 mph (132 km/h)
- MAP is above 26 kPa
- BARO is above 72 kPa
- The fuel level is more than 10 percent

CONDITIONS FOR SETTING THE DTC
- Fuel trim index is above 33%.
- Above conditions present for over 4 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 failure information in the scan tools Freeze Frame and Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm-up cycles without a fault.
- Use a scan tool to 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
- Inspect 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.
- Inspect the power brake booster and valve for leaks.

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:
4. This step indicates that visually and physically inspecting any items which can cause a lean condition can may determine the cause of the DTC being set and save diagnosis time.