Toyota Corolla Repair Manual: Circuit description
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short–term fuel trim and the long–term fuel trim.
The short–term fuel trim is the short–term fuel compensation used to maintain the air–fuel ratio at stoichiometric air–fuel ratio. The signal from the heated oxygen sensor indicates whether the air–fuel ratio is rich or lean compared to the stoichiometric air–fuel ratio. This variance triggers a reduction in the fuel volume if the air–fuel ratio is rich, and an increase in the fuel volume if it is lean.
The long–term fuel trim is the overall fuel compensation carried out in long–term to compensate for a continual deviation of the short–term fuel trim from the central value, due to individual engine differences, wear overtime and changes in the operating environment.
If both the short–term fuel trim and the long–term fuel trim are lean or rich beyond a certain value, it is detected as a malfunction and the mil is illuminated.
|
Dtc no. |
Dtc detection condition |
Trouble area |
| P0171 | When air–fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on lean side (2 trip detection logic) |
|
| P0172 | When air–fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on rich side (2 trip detection logic) |
|
Hint
:
- when dtc p0171 is recorded, the actual air–fuel ratio is on the lean side. When dtc p0172 is recorded, the actual air–fuel ratio is on the rich side.
- If the vehicle runs out of fuel, the air–fuel ratio is lean and dtc p0171 may be recorded. The mil then comes on.
- If the total of the short–term fuel trim value and long–term fuel trim value is within 35 % (engine coolant temperature is more than 75 c (167 f)), the system is functioning normally.
Monitor description
Under the closed–loop fuel control, fuel injection amounts that deviate from the ecm’s estimated fuel amount will cause a change in the long–term fuel trim compensation value. This long–term fuel trim is adjusted when there are persistent deviations in the short–term fuel trim values. And the deviation from a simulated fuel injection amount by the ecm affects a smoothed fuel trim learning value which is the combination of smoothed short–term fuel trim (fuel feedback compensation value) and smoothed long–term fuel trim (learning value of the air–fuel ratio). When the smoothed fuel trim learning value exceeds the dtc threshold, the ecm interprets this as a fault in the fuel system and sets a dtc.
Example: the smoothed fuel trim leaning value is more than +35% or less than –35%, the ecm interprets this as a fail in the fuel system.
Monitor strategy
Typical enabling conditions
Typical malfunction thresholds
Wiring diagram
Refer to dtc p0130
System too lean/rich
Dtc p0171 system too lean (bank 1)
Dtc p0172 system too rich (bank 1) ...
Inspection procedure
Hint:
hand–held tester only:
narrowing down the trouble area is possible by performing ”a/f control” active
test (heated oxygen
sensor or other trouble areas can be distinguished).
Perform ac ...
Other materials:
Vehicle lift and support locations
1. Notice about vehicle condition when jacking up
As a rule, the vehicle must be unloaded when jacking up. Never jack up
or lift up the vehicle loaded
with things of heavy weight.
when removing any parts of heavy weight like the engine and
transmission, the center of gravity of
...
On–vehicle inspection
1. Inspect wireless door lock control functions
Hint:
the switch described in this text is a switch for transmitting
signals (lock switch, unlock switch
and panic switch) which is built into the door control transmitter.
All the functions listed below must be checked in the remote contro ...
Body panel undercoating areas
Apply pastar uwe or pastar uc to the chassis, floor underside, sheet metal
fitting weld points of the body, and
inside of the wheel house to prevent rust and noise, as well as protect the body
from flying rocks.
Hint:
work must be performed while wearing the appropriate protective ...