Possible Causes

PCM sets DTC P0171 or P0174 when it detects fuel system is too lean. Possible causes of a lean fuel system are:

• Insufficient flow or pressure from fuel pump
• Clogged or leaking fuel feed line
• Fuel pressure regulator stuck open
• Clogged fuel filter
• Clogged fuel injector or fuel injector with air inclusion
• Gasoline that does not meet Owner's Manual specification
• Deteriorated Primary HO2S (Sensor 1)
• Insufficient EGR system flow
• An exhaust leak

PCM sets DTC P0172 or P0175 when it detects fuel system is too lean. Possible causes of a rich fuel system are:

• Clogged or stuck closed fuel pressure regulator
• Clogged fuel return pipe
• Leaking fuel injector
• Gasoline that does not meet Owner's Manual specification
• Deteriorated Primary HO2S (Sensor 1)
• EGR System malfunction (too much flow)
• Leaking or stuck open EVAP Canister Purge Valve