LEXUS SC400 1991 Service Repair Manual

NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals M1, M2 and ECU±E of ECU connector.
C
OK
PRemove ECU with connectors still connected.
Measure voltage between terminals M1, M2 and ECU±
E of ECU connector when memory & return switches is
on and off.
Proceed to next circuit inspection shown on matrix chart
(See page SR±52).
2Check memory & return switches.
C
OK
PDisconnect driving position memory & return switches
connector.
Measure resistance between terminals M2, M1 and E of
driving position memory & return switches connector
when memory & return switches is on and off.
Replace memory & return switches.
3Check harness and connector between ECU and memory & return switches (See pa\
ge IN±33).
Repair or replace harness or connector.
Check and replace ECU.
±
STEERING STEERING COLUMNSR±91
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SR±52).
WIRING DIAGRAM
Ignition Switch Circuit
CIRCUIT DESCRIPTION
The ON, OFF signal from the IG switch is sent to the ECU.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±92±
STEERING STEERING COLUMN
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NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal IG of ECU connector and body ground.
C
OK
PRemove ECU with connectors still connected.
Measure voltage between terminal EG of ECU connec-
tor and body ground when ignition switch is on and off.
Proceed to next circuit inspection shown on matrix chart
(See page SR±52.)
2Check ECU±IG fuse.
C
OK
PRemove ECU±IG fuse from J/B No. 1.
Check continuity of ECU±IG fuse.
Continuity
Check for short in all the harness and components con-
nected to ECU±IG fuse.
Check and repair harness or connector between
ECU and battery.
±
STEERING STEERING COLUMNSR±93
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SR±52).
BE±168
.
WIRING DIAGRAM
Park/Neutral Position Switch Circuit
CIRCUIT DESCRIPTION
The park/neutral position switch detects whether the shift position is in P\
position or in another position,
and sends a signal to the ECU.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±94±
STEERING STEERING COLUMN
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OKNG
NGOK
INSPECTION PROCEDURE
1Check shift position indicator.
Check that ªPº lights up on the shift indicator when P position is shif\
ted into, and that ªPº is extin-
guished when shifting into another position.P
Check and repair shift position indicator circuit (See
page BE±168 ).
2Check voltage between terminal P of ECU connector and body ground.
C
OK
PRemove ECU with connectors still connected.
1. Turn ignition switch on.
2. Measure voltage between terminal P of ECU con-
nector and body ground when the shift lever is oper-
ated.
Proceed to next circuit inspection shown on matrix chart
(See page SR±52).
Check for open in harness and connectors be-
tween ECU and [IK1] connector.
±
STEERING STEERING COLUMNSR±95
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WIRING DIAGRAM
CIRCUIT INSPECTION
Parking Brake Switch Circuit
CIRCUIT DESCRIPTION
When the parking brake is operating, the parking brake switch sends a signal\
to the ECU. When this signal
is input to the ECU during tilt & telescopic, the ECU cancels tilt & tel\
escopic.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±96±
STEERING STEERING COLUMN
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OKNG
NGOK
NGOK
OKNG
INSPECTION PROCEDURE
1Check operation of brake warning light.
Check that the brake warning light in the instrument panel comes on when the \
parking brake is opera-
tion with the engine running, and the light goes off when the parking brake is not operating.C
Check brake warning light circuit.
2Input signal check.
C
OK
1. See input signal check.
2. Check the indicator light when the parking brake isoperating.
The indicator light goes off when the parking brake
is operating.
Proceed to next circuit inspection shown on matrix
chart.
3Check voltage between terminal PKB of tilt & telescopic ECU connector and bod\
y ground.
C
OK
PRemove tilt & telescopic ECU with connectors still con-
nected.
1. Turn ignition switch ON.
2. Measure voltage between terminal PKB of tilt & telescopic ECU connector and body ground, when
the parking brake lever is operating.
Proceed to next circuit inspection shown on matrix
chart.
4Check for open in harness and connector between tilt & telescopic ECU and brak\
e warning light
(See page IN±33).
.
Repair or replace harness or connector
Check and replace tilt & telescopic ECU.
±
STEERING STEERING COLUMNSR±97
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SR±52).
WIRING DIAGRAM
Door Courtesy Switch Circuit
CIRCUIT DESCRIPTION
The ECU determines the position of the driver's door by monitoring the voltage at terminal DSW.
 

Door Position 

Switch Position 

DSW Voltage
 Opened Closed Below 1 V
 Closed Opened 10±14 V
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±98±
STEERING STEERING COLUMN
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OKNG
NGOK
INSPECTION PROCEDURE
1Check operation of door courtesy light LH.
Check that door courtesy light comes on when the driver's door is opened, and that the light goes
off when the driver's door is closed.P
Check and repair door courtesy light circuit.
2Check voltage between terminal DSW of ECU connector and body ground.
C
PRemove ECU with connectors still connected.
Measure voltage between terminal DSW of ECU con-
nector and body ground when the driver's door is
opened and closed.
Proceed to next circuit inspection shown on matrix chart
(See page SR±52).
Check for open in harness and connector between
ECU and door courtesy switch LH connector.
±
STEERING STEERING COLUMNSR±99
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SR±52).
IN±33 ).
Unlock Warning Switch Circuit
CIRCUIT DESCRIPTION
Whether or not the key is inserted in the key cylinder is detected and a signal\
is sent to the ECU.
(The switch is ON (closed) when the ignition key is inserted.)
 Ignition key Unlock Warning Switch UWSW Voltage
 

Out 

Opened 

10±14 V
 In Closed Below 1 V
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±100±
STEERING STEERING COLUMN
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