Toyota Celica 2005 Repair Manual page 725

DI−526
MONITOR DESCRIPTION
The evaporative emission system consists of the vapor pressure sensor, the CCV (Canister Closed Valve),
the pressure switching valve and the EVAP VSV (Purge VSV), and those are used to detect malfunctions
in the system by ECM.
This test will run once per driving cycle when the ECM detects stable vapor pressure in the fuel tank. While
the vehicle is being driven on rough or winding roads, the movement of the fuel in the tank will cause unstable
fuel tank vapor pressure and the diagnostic test will not executed.
The ECM performs the following steps:
(a) Closes the CCV. (shuts the system)
(b) Checks the stability of the fuel tank pressure. If the variation in the pressure is greater than the specified
value, disables the diagnosis.
(c) Opens the EVAP VSV to introduce a negative pressure (vacuum) from the intake manifold into the fuel
tank.
(d) Closes the EVAP VSV to seal the fuel tank for storing the negative pressure.
(e) Monitors the negative pressure in the fuel tank for:
(1) Rapid decrease, i.e. a large leak, 0.040 inch or more
(2) Decrease greater than the normal value
If the ECM detects either of the above conditions, the ECM interprets this as a leak in the EVAP system.
The ECM will illuminate the MIL (2−trip detection logic) and set a DTC.
MONITOR STRATEGY
Related DTCs
Required sensors/components
Frequency of operation
Duration
MIL operation
Sequence of operation
2005 CELICA (RM1131U)
DIAGNOSTICS −
P0442
P0456
Main sensors/components
Related sensors/components
Once per driving cycle
60 sec.
2 driving cycles
None
724
ENGINE (2ZZ−GE)
Small leak (0.040 inch or more large hole) is de-
tected
Very small leak (0.020 inch hole) is detected
Vapor pressure sensor
Mass air flow meter, Engine coolant temperature
sensor
EVAP VSV (purge VSV), CCV