Code 55, Fuel Lean Monitor
PCM is capable of determining if fuel system can deliver adequate fuel during power enrichment (heavy acceleration). During power enrichment conditions, PCM expects to see both O2 sensors registering rich. If both sensors do not register rich, Code 55 will set.
Low fuel pressure or restricted fuel flow may cause a lean condition. Check for plugged injectors, poor or contaminated fuel, low fuel level and restricted fuel supply. Vapor lock can also cause Code 55.