The PCM can determine if the engine is running rich when the vehicle operator demands heavy acceleration. When heavy acceleration is demanded, the PCM will go into power enrichment mode. During this mode, a lower air/fuel ratio than 14.7 to 1 (around 12.0 to 1) will be commanded and the fuel injector pulse width On-time will increase. During this condition, the PCM should detect the oxygen sensor 1 (O2S-1) signal voltage go high and remain there. DTC P1171 sets when the PCM is in power enrichment mode and the O2S-1 signal voltage is too low, which is considered lean.

DTC P1171 will set if the O2S-1 voltage is less than 300 mV in power enrichment mode when:

DTC P1171 diagnostic runs continuously once the above conditions have been met.

P1171 is a (type D) DTC

If DTC P0137 is also set, diagnose that DTC first. A short to ground in the O2S-1 signal voltage will also set P1171.

DTC P1171 indicates the engine is running lean in power enrichment mode. To verify the system is running lean in power enrichment, use Scan tool to monitor O2S-1 and HO2S-2 under heavy acceleration. If both sensors are below 300 mV, the system is running lean and the oxygen sensors are probably not at fault.

The following are possible causes of a lean air/fuel mixture: