DIAGNOSIS
- Genera
l
DIAGNOSI
S
GENERA
L
The ECU contains a built-in diagnostic system
.
Depending on the vehicle model, the diagnostic
system has a normal mode only, or it can have a
normal mode and a test mode
.
In the normal mode, the ECU (which is
constantly monitoring most sensors) lights the
"CHECK ENGINE" lamp when it detects a
malfunction in certain sensors or their circuitry
.
At the same time, the ECU registers the system
containing the malfunction in its memory
. This
information is retained in memory even after the
ignition switch is turned off
. When the vehicle is
brought into the shop because of trouble in the
engine control system, the contents of the
memory may be checked to identify the
malfunction
.
"CHECK
ENGINE"
lamp
OHP 9
2
The "CHECK ENGINE" lamp does not light when
certain malfunctions are detected
(
See pages
138 to 140), because those malfunctions would
not cause any major trouble such as engine
stalling
.
After a malfunction is corrected, the "CHECK
ENGINE" lamp turns off
. However, the ECU
memory retains a record of the system in which
the malfunction occurred
.
®
In most engines, the contents of the diagnostic
memory can be checked by connecting terminal
T or TE1 with
El
of the check connector or TDCL
(Toyota diagnostic communication link) and
counting the number of times the "CHECK
ENGINE" lamp blinks
.
OHP 9
2
,-
-rvv
1
r
In the case of OBD-II used for vehicles sold in
the U
.S
.A
. and Canada, an OBD-II scan tool or
TOYOTA hand-held tester is required to read
diagnostic codes (See page
137-2)
.
In some older model engines, the contents of the
diagnostic memory can be checked by
connecting a service wire to terminals T and
El
of the check connector and an analog voltmeter
to terminals VF and
El
of the EFI service
connector, then checking the voltage
fluctuations
.
In recent models, a test mode function has been
added to the functions of the diagnostic system
for the purpose of detecting intermittent problems
(such as poor contact) which are difficult to
detect in the normal mode
.
CHECK
7
ENGIN
E
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131
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