P1171

DTC P1171 Fuel System Lean During Acceleration




Circuit Description
The powertrain control module (PCM) internal circuitry can identify it the vehicle fuel system is capable of supplying adequate amounts of fuel during heavy acceleration (power enrichment). The PCM monitors the voltage of the oxygen sensor during power enrichment. When a power enrichment mode of operation is requested during closed loop operation (by heavy acceleration), the PCM will provide more fuel to the engine. Under these conditions the PCM should detect a rich condition (high oxygen sensor voltage). If this rich exhaust is not detected at this time, a DTC P1171 will set. A plugged fuel filter, restricted fuel line, restricted in-tank filter or defective fuel pump can prevent adequate amounts of fuel from being supplied during power enrichment mode.

Conditions for Setting the DTC
- No related DTCs.
- Engine is operating in closed loop power enrichment mode for 3 seconds.
- Engine coolant temperature is above 60 °C (140 °F).
- While in power enrichment mode the oxygen sensor voltage remains below 400 mV for 3 seconds.

Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp (MIL) the first 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 P1171 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P1171 can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids
- A restricted fuel filter or fuel line, restricted in-tank filter, or a defective fuel pomp may supply adequate amounts of fuel at idle, but may not be able to supply enough fuel during heavy acceleration.
- Water or alcohol in the fuel may cause low HO2S voltage during acceleration.
- Check for faulty or plugged fuel injector(s).
- Check for low fuel.

Steps 1 - 3:

Steps 4 - 6:

Steps 7 - 8:

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
4. When the engine is idling or at steady cruise, the HO2S voltage should vary from between approximately 100 mV to 900 mV. It is possible to measure a satisfactory fuel pressure at idle even though the pressure may drop at high flow requirements. It may be necessary to watch fuel pressure at high engine load.
5. Wrap a shop towel around the fuel pressure connector to absorb any small amount of fuel leakage that may occur when installing gauge. Ignition ON, pump pressure should be 280-320 kPa.
7. Add caution: Use correct pliers so damage to fuel lines will not occur.