The PCM's internal circuitry can identify if the vehicle fuel system is capable of supplying adequate amounts of fuel during heavy acceleration (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. If this "rich" exhaust is not detected at this time, a DTC P1171 will set. A plugged fuel filter or restricted fuel line can prevent adequate amounts of fuel from being supplied during power enrichment mode.

A restricted fuel filter can supply adequate amounts of fuel at idle, but may not be able to supply enough fuel during heavy acceleration. Water or alcohol in fuel may cause low O2S voltage during acceleration. Check for adequate amount of fuel in the fuel tank.

The number below refer to the step number on the diagnostic table.

4. When the engine is idling or at steady cruise, the O2S voltage should vary from between approximately 100 mV to 900 mV. During power enrichment mode, more fuel is needed and O2S voltage should rise above 447 mV. This step checks to see if the O2S is operating properly.