P0171

(_P0171_)
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.

P0106-8 - MAP Sensor
P0135 - Primary HO2S Heater (Sensor 1)
P0137-8 - Secondary HO2S (Sensor 2)
P0141 - Secondary HO2S Heater (Sensor 2)
P0441 - EVAP System Incorrect Purge Flow
P1259 - VTEC System

Possible Cause
DTC P0171
System too lean
- 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
- Valve Clearance too tight
- Exhaust leak