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): Description

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 (A/F) 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 trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and 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)	Air induction system Injector for port injection Injector for direct injection Mass Air Flow (MAF) meter (bank 1, 2) Engine Coolant Temperature (ECT) sensor Fuel pressure Gas leakage from exhaust system Open or short in A/F sensor (bank 1, 2 sensor 1) circuit A/F sensor(bank 1, 2 sensor 1) A/F sensor heater (bank 1, 2 sensor 1) A/F sensor heater circuits Ventilation valve and hose Ventilation hose connections ECM
P0172 P0175	Fuel trim is too rich (2 trip detection logic)	MAF meter ECT sensor Injector for port injection Injector for direct injection Ignition system Fuel pressure Gas leakage from exhaust system Open or short in A/F sensor (bank 1, 2 sensor 1) circuit A/F sensor(bank 1, 2 sensor 1) A/F sensor heater (bank 1, 2 sensor 1) A/F sensor heater circuits ECM

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.