P0171
DTC P0171 System Too Lean (Bank 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 powertrain control module (PCM) monitors the Bank 1 HO2S 1 signal and adjusts fuel delivery based upon the HO2S 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 a Tech 2. Ideal fuel trim values are around 0 %; if the HO2S signal indicates a lean condition the PCM will add fuel, resulting in fuel trim values above 0 %. If a rich condition is detected, the fuel trim values will be below 0 %, indicating that the PCM is reducing the amount of fuel delivered. If an excessively lean condition is detected on Bank 1, the PCM will set Diagnostic Trouble Code P0171. DTC P0171 is a type B code.
The PCM's maximum authority to control long term fuel trim allows a range between -14% and +20%. The PCM monitors fuel trim under various engine speed/load fuel trim cells before determining the status of the fuel trim diagnostic.
Conditions for Setting the DTC
- No Tech 2 test is being run.
- None of the following: EGR Diagnostic Trouble Codes, HO2S Diagnostic Trouble Codes, (response, transition, open, low volts, no activity), TP sensor Diagnostic Trouble Codes, MAP Diagnostic Trouble Codes, IAT Diagnostic Trouble Codes, canister purge Diagnostic Trouble Codes, EVAP Diagnostic Trouble Codes, injector circuit Diagnostic Trouble Codes or misfire Diagnostic Trouble Codes.
- Engine coolant temperature is between 65 °C (149 °F) and 104 °C (219 °F).
- Intake air temperature is between -40 °C (-40 °F) and 120 °C (248 °F).
- Manifold absolute pressure is between 23.75 kPa and 99 kPa.
- Engine speed is between 400 and 6000 RPM.
- Barometric pressure is greater than 72.3 kPa.
- System voltage is greater than 9.5 V.
- Engine is operating in "Closed Loop".
- The average of the short term fuel trim samples is greater than 0.97 and the average of adaptive index multiplier samples is greater than 1.21.
Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) after the second consecutive trip in which the fault is detected.
- The PCM will store conditions which were present when the Diagnostic Trouble Code was set as Freeze Frame and in the Failure Records data.
Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A history Diagnostic Trouble Code P0171 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- Diagnostic Trouble Code P0171 can be cleared by using the Scan Tool's "Clear Info" function.
Diagnostic Aids
Check for the following conditions:
- Poor connection at PCM - Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.
- Damaged harness - Inspect the wiring harness for damage; shorts to ground, shorts to battery positive and open circuits. If the harness appears to be OK, observe the Bank 1 HO2S 1 display on the Tech 2 while moving connectors and wiring harnesses related to the engine harness. A change in the display will indicate the location of the fault.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the Diagnostic Trouble Code to be set occurs. This may assist in diagnosing the condition.
Steps 1 - 2:
Step 3 - 6:
Steps 7 - 11:
Steps 12 - 16:
Steps 17 - 18:
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart:
2. Diagnostic Trouble Codes other than P0171 may indicate a condition present which may cause a lean condition. If this is the case, repairing the condition which caused the other Diagnostic Trouble Code will most likely correct the Diagnostic Trouble Code P0171.
4. If the Diagnostic Trouble Code P0171 test passes while the Failure Records conditions are being duplicated, the lean condition is intermittent. Refer to Diagnostic Aids or Symptoms for additional information on diagnosing intermittent problems.