1991 LEXUS SC400 relay

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Page 2735 of 4087

LEXUS SC400 1991  Service Repair Manual 
ECU Power Source Circuit
CIRCUIT DESCRIPTION
When the ignition switch is turned on, battery voltage
is applied to the terminal IG SW of the ECU, and the
main relay control circuit in the ECU sends a

Page 2736 of 4087

LEXUS SC400 1991  Service Repair Manual 
DIAGNOSTIC CHART
DIAGNOSTIC
 CHART
Check for short in all the harness and
components connected to IGN fuse.
Check voltage of terminal M±REL.
Check for open in harness and connector
between battery a

Page 2740 of 4087

LEXUS SC400 1991  Service Repair Manual 
OKNG
OKNG
8Check EFI main relay.
C
OK
P
C
OK
Remove EFI main relay.
Check continuity between terminals of EFI main relay
shown below.
(2) Apply battery voltage between terminals 1 and 3.
(2) Check co

Page 2743 of 4087

LEXUS SC400 1991  Service Repair Manual 
Injector Circuit
CIRCUIT DESCRIPTION
The injectors are provided to the intake manifold. They inject fuel into th\
e cylinders based on the signals from
the engine & ECT ECU.
DIAGNOSTIC CHARTDIAGNOSTI

Page 2745 of 4087

LEXUS SC400 1991  Service Repair Manual 
NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals #20 ~ 40 of engine & ECT ECU and body ground.\
C
OK
P(2) Connect the Check Harness A.(See page  TR±30)
(2) Turn ignition switch on.
M

Page 2746 of 4087

LEXUS SC400 1991  Service Repair Manual 
OKNG
OKNG
OKNG
3Check for open in harness and connector between terminal E01, E02 of eng\
ine & ECT ECU con-
nector and body ground (See page  IN±27).
Repair or replace harness or connector.
4Check

Page 2751 of 4087

LEXUS SC400 1991  Service Repair Manual 
ISC Valve Circuit
CIRCUIT DESCRIPTION
The ISC valve is provided on the intake air chamber and in-
take air bypassing the throttle valve is directed to the ISC
valve through a hose.
A step motor is bu

Page 2752 of 4087

LEXUS SC400 1991  Service Repair Manual 
OKNG
OKNG
INSPECTION PROCEDURE
1Check ISC value.
C
OK
P
P
OK
C
Disconnect ISC connector.
Measure resistance between terminals shown below.
Remove ISC Valve
(2) Connect  the battery positive lead to t