P0171
DTC P0171 Fuel Trim 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 and Bank 2 HO2S 1 signals and adjusts fuel delivery based upon the HO2S signal voltages. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim values are around 0%; if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in fuel trim values above 0%. It 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 DTC P0171.
The PCM's maximum authority to control long term fuel trim allows a range between -15% (automatic transmission) or -12% (manual transmission) and +20%. The PCM monitors fuel trim under various engine speed/load fuel trim cells before determining the status the fuel trim diagnostic.
Conditions for Setting the DTC
- No scan tool test is being run.
- None of the following: EGR DTCs, HO2S DTCs, (response, transition, open, low volts, no activity), MAF DTCs, TP sensor DTCs, MAP DTCs, IAT DTCs, canister purge DTCs, EVAP DTCs, injector circuit DTCs, or misfire DTCs.
- Engine coolant temperature is between 25 °C (77 °F) and 100 °C (212 °F).
- Intake air temperature is between -40 °C (-40 °F) and 120 °C (248 °F).
- Manifold absolute pressure is between 24 kPa and 99 kPa.
- Throttle angle is steady below 95%.
- Vehicle speed is below 136 kph (85 mph).
- Engine speed is between 400 and 6000 RPM.
- Barometric pressure is greater than 72.5 kPa.
- Mass air flow (MAF) is between 2 g/second and 200 g/second.
- Ignition voltage is above 9.5 volts.
- Fuel system is in closed loop.
- Canister purge duty cycle is greater than 0% if on.
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 DTC 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 DTC P01 71 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P0171 can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.
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. If the harness appears to be OK, observe the Bank 1 HO2S 1 display on the scan tool 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 DTC to be set occurs. This may assist in diagnosing the condition.
Steps 1 - 6:
Steps 7 - 12:
Steps 13 - 19:
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
2. DTCs other than P0171 and P0174 may indicate a condition present which may cause a lean condition. If this is the case, repairing the condition which caused the other DTC will most likely correct the DTC P0171 1P0174.
4. If the DTC P0171 test passes while the Failure Records conditions are being duplicated, the lean condition is intermittent. For additional information on diagnosing intermittent problems, refer to Diagnostic Aids or Symptoms.