1991 LEXUS SC400 relay

WIRING DIAGRAM
DTC51ABS Pump Motor Lock
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
51Pump motor is not operating normally duringinitial
check.
ABS pump motor
Fail safe function: If trouble occurs in the ABS pump motor, the ECU cuts off the current to the solenoid
relay and prohibits ABS control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
See inspection of ABS pump motor (See page BR±65 or BR±68 ).
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±125
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BR±228
WIRING DIAGRAM
DTC54Excessive Operation of TRAC Pump Motor
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
54
TRAC motor relay ON is output continuously10 times
at intervals of less than 24 sec.when traction control is
not being executed.
TRAC Actuator

TRAC Accumulator

Brake fluid leakage

ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±130±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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WIRING DIAGRAM
DTC55Brake Fluid Level Warning Switch Circuit
CIRCUIT DESCRIPTION
The brake fluid level warning switch sends the appropriate signal to the EC\
U when the brake fluid level drops.
DTC No.DTC Detecting ConditionTrouble Area
55Voltage at ECU terminal LBL is 0Vcontinuously for 10
sec. or more.

Brake fluid level.

Brake fluid level warning switch.

Short in brake fluid level warning switchcircuit.

ECU
Fail safe function: If trouble occurs in this circuit, the ECU cuts off current to the TRAC solenoid relay
and prohibits TRAC control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±132±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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DTC56, 57Pressure Sensor Circuit
CIRCUIT DESCRIPTION
The pressure sensor detects the TRAC accumulator hydraulic pressure and if \
it is low, it sends signals to the
ECU to operate the pump. If the pressure is high, it sends signals to th\
e ECU to stop the pump.
DTC No.DTC Detecting ConditionTrouble Area
56Pressure sensor terminal PR outputs below 1 V for
about 1 sec. or more.
Open or short in pressure sensor circuit.
57
TRAC (BRAKE) control is executed continuouslymore
than 255 times while pressure sensor ONsignal is not
output.

Pressure sensor
Fail safe function: If trouble occurs in the pressure sensor circuit, the ECU cuts off current to the TRAC
solenoid relay and prohibits TRAC control.
BR±134
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKNG
OKNG
INSPECTION PROCEDURE
1Check ABS warning light.
See Combination Meter Troubleshooting on page BE±159.
Replace bulb or combination meter assembly.
2Check ABS solenoid relay.
C
OK
P
OK
C
Remove solenoid relay from R/B No. 6.
Check continuity between each terminal of ABS sole-
noid relay shown below.
1. Apply battery voltage between terminals 4 and 6.
2. Check continuity between each terminal of ABS so-
lenoid relay shown below.
Replace ABS solenoid relay.
Repair or replace and check for open in harness and connector between ch\
eck connector and ABS
solenoid relay and body ground (See page IN±33).
BR±146±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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NOYES
YESNO
OKNG
INSPECTION PROCEDURE
3Is diagnosis trouble code output?
Perform diagnostic trouble code check on page BR±76.
Repair circuit indicated by the code output.
4Does ABS warning light go off if short pin is removed?
Check for short in harness and connector between warn-
ing light and data link connector 1 and ECU (See page
IN±33 ).
5Check ABS solenoid relay (See step No. ).
Replace ABS solenoid relay.
Repair or replace and check for short in harness
and connector between data link connector 1 and
ABS solenoid relay (See page IN±33).
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±147
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Fuel Pump ECUAuto Antenna Motor and Relay
Power Seat ECU
(For Passenger's Seat)
Power Seat ECU
(For Driver's Seat) CD Automatic Changer
Wireless Door Lock ECU
Moon Roof Control Relay
Locations of ECUs (Cont'd)
Many ECUs are mounted in this vehicle.
Take the following precautions during body repair to prevent damage to th\
e ECUs.


Before starting electric welding operations, disconnect the negative (-\
) terminal cable from the battery.
When the negative (-) terminal cable is disconnected from the battery, memory of the clock and audio
systems will be cancelled. So before starting work, make a record of the\
contents memorized by each
memory system. Then when work is finished, reset the clock and audio sys\
tems as before.
When the vehicle has tilt and telescopic steering, power seat and outsid\
e rear view mirror, which are all
equipped with memory function, it is not possible to make a record of th\
e memory contents.
So when the operation is finished, it will be necessary to explain this \
fact to the customer, and request
the customer to adjust the features and reset the memory.

Do not expose the ECUs to ambient temperatures above 80 °C (176 °F).
NOTICE: If it is possible the ambient temperature may reach 80°C (176°F) or, more, remove the ECUs
from the vehicle before starting work.

Be careful not to drop the ECUs and not to apply physical shocks to them\
.
5. COMPONENTS ADJACENT TO THE BODY PANELS
Various types of component parts are mounted directly on or adjacently to\
the body panels.
Strictly observe the following precautions to prevent damaging these com\
ponents and the body panels
during handling.

Before repairing the body panels, remove their adjacent components or ap\
ply protective covers over
the components.

Before prying components off using a screwdriver or a scraper, etc., attach protective tape to the tool
tip or blade to prevent damaging the components and the body paint.

Before removing components from the outer surface of the body, attach protective tape to the body to
ensure no damage to painted areas.
HINT: Apply touch-up paint to any damaged paint surfaces.

Before drilling or cutting sections, make sure that there are no wires, \
hoses, etc., on the reverse side.
INTRODUCTIONIN-9
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EFI Main Relay
INSPECTION OF EFI MAIN RELAY
1. REMOVE EFI MAIN RELAY FROM RELAY BOX IN ENGINE
COMPARTMENT
2. INSPECT EFI MAIN RELAY
A. Inspect relay continuity (a) Using an ohmmeter, check that there is continuitybetween terminals 1 and 3.
(b) Check that there is no continuity between terminals 2 and 4.
If continuity is not as specified, replace the relay.
B. Inspect relay operation (a) Apply battery voltage across terminals 1 and 3.
(b) Using an ohmmeter, check that there is continuitybetween terminals 2 and 4.
If operation is not as specified, replace the relay.
3. REINSTALL EFI MAIN RELAY
FI±64
±
EFI SYSTEM Electronic Control System (EFI main RelaY)
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