P0171
DTC P0171 Fuel Trim System LeanSystem 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 the short term fuel trim values will indicate a change made to the fuel delivery system. The ideal fuel trim values are around 128 (0%). 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%). Whenever a rich condition is detected, the fuel trim values will read below 128 (0 to -100%), indicating that the PCM is reducing the amount of fuel. Whenever the exhaust emissions reach an excessive level due to a lean condition, a fuel trim DTC is set.
Conditions for Running the DTC
- DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, and P1441, not set.
- 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 550 RPM and 3400 RPM.
- Vehicle speed is below 82 mph (132 kmph).
- MAP is above 28 kPa.
- BARO is greater than 72 kPa.
- EVAP purge is not occurring.
Conditions for Setting the DTC
- Fuel Trim Index is above 170 (33%).
- Above conditions present for over 4 seconds.
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
- 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.
- Check the brake power booster check valve.
Steps 1 - 2:
Steps 3 - 4:
Step 5:
Steps 6 - 9:
Steps 10 - 12:
Steps 13 - 14:
Steps 15 - 17:
Test Description
The number(s) below refer(s) to the step number(s) 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 information then stores on the scan tool for later reference.
5. This step indicates that visually/physically checking any items which can cause a lean condition can determine the cause of the DTC being set and save diagnosis time.
9. A vacuum leak can change the Fuel Trim Index and set DTC P0171. This step checks the intake manifold for vacuum leaks.
11. Contaminants in fuel, such as alcohol or water, can create a lean condition setting DTC P0171. Checking for these contaminants could identify the malfunction.
17. If no malfunction has been present at this point and no additional DTCs were set, refer to Diagnostic Aids for any additional checks and for information.