Too Lean

The scan tool indicates Diagnostic Trouble Code (DTC) P0171: The fuel system is too lean.

Description
By monitoring the Long Term Fuel Trim, long term malfunctions in the fuel system will be detected. If a malfunction has been detected during two consecutive trips, the MIL will come on and DTC P0171 and/or P0172 will be stored.

NOTE: If some of the DTCs listed below are stored at the same time as DTC P0171 and/or P0172, troubleshoot those DTCs first, then troubleshoot DTC P0171 and/or P0172.

P0107,P0108, P1128, P1129: MAP Sensor
P0135: Primary HO2S (Sensor 1) Heater
P0137, P0138: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) Heater
P0401: EGR Flow Insufficient
P1259: VTEC System
P1491: EGR Valve Lift Insufficient
P1498: EGR Valve Lift Sensor High Voltage

Possible Cause
- Fuel Pump insufficient flow/pressure
- Fuel Feed Line clogged, leaking
- Fuel Pressure Regulator stuck open
- Fuel Filter clogged
- Fuel Injector clogged, air inclusion
- Gasoline doesn't meet Owner's Manual spec.
- Primary HO2S (Sensor 1) deteriorated
- MAP Sensor range/performance
- EGR System malfunction (too much flow)
- Valve Clearance
- Exhaust leak