Diagnostic Aids

Ensure fuel pressure is within specifications. Fuel pressure that is too low will cause a lean condition. Check for vacuum and exhaust leaks. Check MAP sensor for correct values. A MAP sensor that reads high vacuum will cause a lean condition. When MAP sensor is disconnected, PCM will substitute a default value. If lean condition goes away, replace MAP sensor and recheck system. Check for fuel contamination. Small amounts of water in fuel tank can cause DTC P0171 to set. Check HO2S for silicone and other contaminants.

Check for a poor PCM electrical connection. An intermittent malfunction may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, or poor terminal-to-wire connections before component replacement.