Toyota Celica 2005 Repair Manual page 495

DI−296
2005 CELICA (RM1131U)
DIAGNOSTICS − ENGINE (2ZZ−GE)
The diagnosis system operates in "normal mode"
S
during normal vehicle use. In "normal mode", 2 trip
detection logic* is used to ensure accurate detec-
tion of malfunctions. A "check mode" is also avail-
able to technicians as an option. In "check mode",
1 trip detection logic is used for simulating malfunc-
tion symptoms and increasing the system's ability to
detect malfunctions, including intermittent malfunc-
tions (hand−held tester only) (See step 3).
*2 trip detection logic:
S
When a malfunction is first detected, the malfunc-
tion is temporarily stored in the ECM memory. This
is known as 1st trip detection. If the ignition switch
is turned OFF and then ON again, and the same
malfunction is detected again, the MIL will illumi-
nate. This is known as 2nd trip detection.
Freeze frame data:
S
The freeze frame data records the engine condi-
tions (fuel system, calculated load, engine coolant
temperature, fuel trim, engine speed, vehicle
speed, etc.) when a malfunction is detected. When
troubleshooting, freeze frame data can help deter-
mining if the vehicle was running or stopped, if the
engine was warmed up or not, if the air−fuel ratio
was lean or rich, as well as other data from the time
when a malfunction occurred.
Priorities for troubleshooting:
When multiple DTCs occur, find out the order in which the DTCs
should be inspected by checking the component's DTC chart.
If no instructions are written in the DTC chart, check DTCs in the
following order of priority:
(1) DTCs other than fuel trim malfunction DTCs (P0171
and P0172) and misfire DTCs (P0300 to P0304).
(2) Fuel trim malfunction DTCs (P0171 and P0172).
(3) Misfire DTCs (P0300 to P0304).
494