± DIAGNOSTICSENGINE
DI±165
359 Author: Date:
2005 SEQUOIA (RM1146U)
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)
CIRCUIT DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim con-
sists of both the short±term and long±term fuel trims.
The short±term fuel trim is fuel compensation that is used to constantly maintain the air±fuel ratio at stoichio-
metric 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 central value. The long±term fuel trim, which controls overall fuel com-
pensation, compensates for long±term deviations in the fuel trim from the central value caused by the short±
term fuel trim compensation.
If both the short±term 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.
DIDFQ±01
