P1171

DTC P1171 Fuel System Lean During Acceleration




Circuit Description
The powertrain control module (PCM) internal circuitry can identify if 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 Diagnostic Trouble Code P1171 will set. A plugged fuel filter or restricted fuel line can prevent adequate amounts of fuel from being supplied during power enrichment mode. DTC P1171 is a type A code.

Conditions for Setting the DTC
- No related Diagnostic Trouble Codes.
- Engine is operating in "Closed Loop".
- 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 time 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 P1171 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- Diagnostic Trouble Code P1171 can be cleared by using the Scan Tool's "Clear Info" function.

Diagnostic Aids
- A restricted fuel filter or fuel line can 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 - 5:

Steps 6 - 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. During "power enrichment" mode, more fuel is needed and the HO2S voltage should rise above 447 mV. This step checks to see if the HO2S is operating properly.
5. Wrap a shop towel around the fuel pressure connector to absorb any small amount of fuel leakage that may occur when installing the gauge. Ignition ON, pump pressure should be 235 - 320 kPa.
7. Add Caution: Use correct pliers so damage to fuel lines will not occur.