P0171

Fuel Supply System

PO171 The scan tool indicates Diagnostic Trouble Code (DTC) P0171: The fuel system is too lean [Right Bank (Bank 1)].
PO172 The scan tool indicates Diagnostic Trouble Code (DTC) PO172: The fuel system is too rich [Right Bank (Bank 1)].
PO174 The scan tool indicates Diagnostic Trouble Code (DTC) PO174: The fuel system is too lean (Left Bank (Bank 2)].
PO175 The scan tool indicates Diagnostic Trouble Code (DTC) P0175: The fuel system is too rich [Left Bank (Bank 2)].

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, P0172, P0174 and/or P0175 will be stored.

NOTE: If some of the DTCs listed below are stored at the same time as DTC P0171, P0172, P0174 and/or P0175, troubleshoot those DTCs first, then troubleshoot DTC P0171, P0172, P0174 and/or P0175.

P0106*1, P0107, P0108, Pi 128*2, Pi 129*2: MAP Sensor
P0135: Right Primary HO2S Heater (Bank 1, Sensor 1)
P0137, P0138: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S Heater (Sensor 2)
P0155: Left Primary HO2S Heater (Bank 2, Sensor 1)
PO4O1: EGR Flow Insufficient
P1491: EGR Valve Lift Insufficient
P1498: EGR Valve Lift Sensor High Voltage
*1: '96 model only
*2: '97 model only

Possible Cause

DTC P0171, P0174
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*1
^ EGR System insufficient flow
^ Exhaust leak

DTC P0172, P0175
System too rich

^ Fuel Pressure Regulator clogged, stuck closed
^ Fuel Return Pipe clogged
^ Fuel Injector leaking
^ Gasoline doesn't meet Owner's Manual spec.
^ Primary HO2S (Sensor 1) deteriorated
^ MAP Sensor range/performance*1
^ EGR System malfunction (too much flow)
^ EVAP Purge Control Solenoid Valve leaking, stuck opened