Diagnostic Aids

If problem can not be isolated using diagnostic charts, monitor LT fuel trim and fuel trim cell while operating vehicle under various loads. This may isolate condition which caused Code P0171 to set.

A condition that causes Code P0300 (MISFIRE DETECTED) may also set Code P0171. An extremely lean condition which sets Code P0171 can cause a misfire at idle and Code P0300 to set. If cause of Code P0171 can not be determined and Code P0300 is also set, refer to Code P0300 chart.