Toyota Camry Manual page 1299

DI–272
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 heated oxygen sensor indicates whether the air–fuel ratio is RICH or
LEAN compared to the ideal theoretical value, triggering a reduction in fuel volume if the air–fuel ratio is rich,
and an increase in fuel volume if it is lean.
Long–term fuel trim is overall fuel compensation carried out long–term to compensate for continual deviation
of the short–term fuel trim from the central value due to individual engine differences, wear over time and
changes in the usage environment.
If both the short–term fuel trim and long–term fuel trim are LEAN or RICH beyond 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)
HINT:
D
When DTC P0171 is recorded, the actual air–fuel ratio is on the LEAN side. When DTC P0172 is re-
corded, the actual air–fuel ratio is on the RICH side.
D
If the vehicle runs out of fuel, the air–fuel ratio is LEAN and DTC P0171 is recorded. The MIL then
comes on.
D
If the total of the short–term fuel trim value and long–term fuel trim value is within
or more), the system is functioning normally.
INSPECTION PROCEDURE
HINT:
Read freeze frame data using TOYOTA hand–held tester or OBD II scan tool. Because freeze frame records
the engine conditions when the malfunction is detected, when troubleshooting it is useful for determining
whether the vehicle was running or stopped, the engine warmed up or not, the air–fuel ratio lean or rich, etc.
at the time of the malfunction.
DIAGNOSTICS
System too Lean (Fuel Trim)
(Except California Spec.)
System too Rich (Fuel Trim)
(Except California Spec.)
DTC Detecting Condition
– ENGINE (1MZ–FE)
D Air intake (hose loose)
D Fuel line pressure
D Injector blockage
D Heated oxygen sensors (bank 1, 2 sensor 1) malfunction
D Mass air flow meter
D Engine coolant temp. sensor
D Gas leakage on exhaust system
D Fuel line pressure
D Injector leak, blockage
D Heated oxygen sensors (bank 1, 2 sensor 1) malfunction
D Mass air flow meter
D Engine coolant temp. sensor
D Gas leakage on exhaust system
Author :
Trouble Area
35 % (80°C (176°F)
Date :
DI4DR–01
507