DTC P0171 System Too Lean (Bank 1); DTC P0172 System Too Rich (Bank 1); DTC P0174 System Too Lean (Bank 2); DTC P0175 System Too Rich (Bank 2); DTC P1170 Port Injector Fuel Performance; DTC P117B Direct Injector Fuel Performance: Description

WARNING: This page is about a different car, the 2008 Lexus IS F. However, it is still accessible from the selected car via links, so may be relevant.

The fuel trim is related to the feedback compensation value, not to the basic injection time The fuel trim consists of both the short-term and the long-term fuel trim

The short-term fuel trim is fuel compensation that is used to constantly maintain the air fuel ratio at stoichiometric levels. The signal from the air fuel ratio sensor indicates whether the air fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air fuel ratio is rich and an increase in the fuel injection volume if it is lean

Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the ideal theoretical value The long-term fuel trim controls overall fuel compensation The long-term fuel trim compensates for long term deviations of the fuel trim from the ideal theoretical value These long term deviations result from the corrections made by the short-term fuel trim

If both the short-term fuel and long-term fuel trim are lean or rich beyond predetermined values, it is interpreted as a malfunction, the ECM illuminates the MIL and sets a DTC.

DTC DETECTION CONDITION CHART

DTC No.	DTC Detection Condition	Trouble Area
P0171 P0174	Fuel trim is too lean (2 trip detection logic)	Intake system Fuel injector assembly for port injection Fuel injector assembly for direct injection Mass air flow meter sub-assembly Engine coolant temperature sensor Fuel pressure Gas leaks from exhaust system Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit Air fuel ratio sensor (bank 1, 2 sensor 1) Air fuel ratio sensor heater (bank 1, 2 sensor 1) Air fuel ratio sensor (bank 1, 2 sensor 1) heater circuits PCV valve and hose PCV hose connections ECM
P0172 P0175	Fuel trim is too rich (2 trip detection logic)	Mass air flow meter sub-assembly Engine coolant temperature sensor Fuel injector assembly for port injection Fuel injector assembly for direct injection Ignition system Fuel pressure Gas leaks from exhaust system Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit Air fuel ratio sensor (bank 1, 2 sensor 1) Air fuel ratio sensor heater (bank 1, 2 sensor 1) Air fuel ratio sensor heater (bank 1, 2 sensor 1) circuits ECM
P1170	With stable air fuel ratio feedback, a fuel injection system malfunction has been detected and fuel trim of the port injection is unusually rich or lean side	Fuel injector assembly for port injection Fuel injector assembly for direct injection Fuel pressure ECM
P117B	With stable air fuel ratio feedback, a fuel injection system malfunction has been detected and fuel trim of the direct injection is unusually rich or lean side

HINT

If the vehicle runs out of fuel, the air fuel ratio is lean and DTC P0171 or P0174 may be set. The MIL is then illuminated