Toyota Camry Manual page 1294

DTC P0171
DTC P0172
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared against the basic injection time. Fuel trim
includes short–term fuel trim and long–term fuel trim.
Short–term fuel trim is the short–term fuel compensation used to maintain the air–fuel ratio at its ideal
theoretical value.
The signal from the A/F sensor is approximately proportional to the existing air–fuel ratio, and ECM compar-
ing it with the ideal theoretical value, the ECM reduces fuel volume immediately if the air–fuel ratio is rich
and increases fuel volume if it is lean.
Long–term fuel trim compensates the deviation from the central value of the short–term fuel trim stored up
by each engine tolerance, and the deviation from the central value due to the passage of time and changes
of using environment.
If both the short–term fuel trim and long–term fuel trim exceed a certain value, it is detected as a malfunction
and the MIL lights up.
DTC No.
When air fuel ratio feedback is stable after engine warming up,
P0171 fuel trim is considerably in error on RICH side
(2 trip detection logic)
When air fuel ratio feedback is stable after engine warming up,
P0172 fuel trim is considerably in error on LEAN side
(2 trip detection logic)
DIAGNOSTICS
System too Lean (Fuel Trim)
(Only for California Spec.)
System too Rich (Fuel Trim)
(Only for California Spec.)
DTC Detecting Condition
– ENGINE (1MZ–FE)
D Gas leakage on exhaust system
D Air intake (hose loose)
D Fuel line pressure
D Injector blockage
D Mass air flow meter
D Engine coolant temp. sensor
D A/F sensors (bank 1, 2 sensor 1)
D Gas leakage on exhaust system
D Fuel line pressure
D Injector leak, blockage
D Mass air flow meter
D Engine coolant temp. sensor
D A/F sensors (bank 1, 2 sensor 1)
Author :
Trouble Area
Date :
DI–267
DI07R–05
502