Toyota Celica 2005 Repair Manual page 646

MONITOR DESCRIPTION
Fuel compensation
amount
A20489
Under 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. The smoothed fuel trim learning
value 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 val-
ue exceeds the DTC threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.
Example:
If the smoothed fuel trim learning value is more than +35% or less than −35%, the ECM interprets this as
a malfunction in the fuel system.
MONITOR STRATEGY
Related DTCs
Required sensors/components
Frequency of operation
Duration
MIL operation
Sequence of operation
2005 CELICA (RM1131U)
DIAGNOSTICS
1.35
1.0
0.65
Main sensors/components
Related sensors/components
Continuous
10 sec.
2 driving cycles
None
− ENGINE (2ZZ−GE)
P0171
P0172
645
+35 (%): Threshold at LEAN
−35 (%): Threshold at RICH
Fuel system lean (Bank 1)
Fuel system rich (Bank 1)
Front oxygen sensor
Engine coolant temperature sensor, Mass air flow
meter, Crankshaft position sensor
DI−447
A21204