Lexus SC300 / Lexus SC400. Service manual — part 201

Check for Voltage

(a) Establish conditions in which voltage is present at the

check point.

Example:
(A)–Ignition SW on
(B)–Ignition SW and SW 1 on
(C)–Ignition SW, SW 1 and Relay on (SW 2 off)
(b) Using a voltmeter, connect the negative (–) lead to a

good ground point or negative (–) battery terminal and
the positive (+) lead to the connector or component
terminal. This check can be done with a test bulb instead
of a voltmeter.

Check for Continuity and Resistance

(a) Disconnect the battery terminal or wire so there is no

voltage between the check points.

(b) Connect the two leads of an ohmmeter to each of the

check points.

If the circuit has diodes, reverse the two leads and check
again.
When contacting the negative (–) lead to the diode positive
(+) side and the positive (+) lead to the negative (–) side,
there should be continuity. When contacting the two leads in
reverse, there should be no continuity.
HINT: Specifications may vary depending on the type of tes-
ter, so refer to the tester’s instruction manual before perform-
ing the inspection.

Check LED (Light Emitting Diode) in the same manner as that
for diodes.
HINT:

•

Use a tester with a power source of 3 V or greater to
overcome the circuit resistance.

•

If a suitable tester is not available, apply battery voltage
and check that the LED lights up.

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BODY ELECTRICAL SYSTEM

General Information

BE–5

(c) Use a volt/ohmmeter with high impedance (10 k/V

minimum) for troubleshooting of the electrical circuit.

Check the Bulb

(a) Remove the bulb.
(b) There

should be continuity between the respective

terminals of the bulb together with a certain amount of
resistance.

(c) Apply the two leads of the ohmmeter to each of the

terminals.

(d) Apply battery voltage and check that the bulb light up.

Check for Short Circuit

(a) Remove the blown fuse and eliminate all loads from the

fuse.

(b) Connect a test bulb in place of the fuse.
(c) Establish conditions in which the test bulb comes on.
Example:
(A)–Ignition SW on
(B)–Ignition SW and SW 1 on
(C)–Ignition SW, SW 1 and Relay on (Connect the Relay) and

SW 2 off (or Disconnect SW 2)

(d) Disconnect and reconnect the connectors while

watching the test bulb. The short lies between the
connector where the test bulb stays lit and the connector
where the bulb goes out.

(e) Find the exact location of the short by lightly shaking the

problem wire along the body.

BE–6

–

BODY ELECTRICAL SYSTEM

General Information

PRECAUTIONS

Take care to observe the following precautions when performing inspections or removal and replacement
of body electrical related parts.

1. SRS AIR–BAG SYSTEM

Work must be started approx. 20 seconds after the ignition is set to the Lock position and the negative
(–) terminal cable is disconnected from the battery. (See page

AB–2

)

When disconnecting any of the connectors in the SRS AIR–BAG system, be sure to Lock the ignition
switch and disconnect the battery negative (–) terminal first. Since the connectors are twin lock type
connectors, disconnect the connectors only after releasing the first stage lock.

When connecting SRS AIR–BAG system connectors, be sure to lock them securely. (If the connectors
are not locked securely, the system may not operate when needed.)

Always store the steering wheel pad with the pad surface facing upward. (Storing the pad with its
metallic surface up may lead to a serious accident if the air bag inflates for some reason.)

When installing the spiral cable, be sure the vehicle is in the straight ahead condition and confirm that
the spiral cable is in the neutral position when it is installed. (See page

BE–40

)

INFORMATION LABELS (NOTICE) are attached to the periphery of the air bag components. Follow
the NOTICE.

2. MICRO COMPUTER PRESET DRIVING POSITION SYSTEM

Power Seat Control System
Power Mirror Control System
Power Tilt and Telescopic Steering System

If the battery negative (–) terminal is disconnected, the preset driving positions stored in memory are
erased, so be sure to note the positions and reset them after the battery terminal is reconnected.

3. AUDIO SYSTEM

If the battery negative (–) terminal is disconnected, the preset AM, FM 1 and FM 2 stations stored in
memory are erased, so be sure to note the stations and reset them after the battery terminal is
reconnected.

If the battery negative (–) terminal is disconnected, the ”ANTI–THEFT SYSTEM” will operate when
the terminal is reconnected, but the radio, tape player and CD player will not operate. Be sure to input
the correct ID number so that the radio, tape player and CD player can be operated again.

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BODY ELECTRICAL SYSTEM

Precautions

BE–7

PREPARATION

SST (SPECIAL SERVICE TOOLS)

Illustration

Part No.

Part Name

Note

09213–31021

Crankshaft Pulley
Puller

For removing steering wheel

RECOMMENDED TOOLS

Illustration

Part No.

Part Name

Note

09082–00015

TOYOTA
Electrical Tester

09041–0030

Torx Driver
T30

For removing and installing steering wheel pad and
power window motor

09042–00010

Torx Socket
T30

For removing and installing steering wheel pad and
power window motor

EQUIPMENT

Part Name

Note

Voltmeter

Ammeter

Ohmmeter

Test lead

Thermometer

Water temperature sender gauge, Engine oil level, Warning switch, Seat heater

Syphon

Brake fluid level warning switch

Oil bath

Engine oil level warning switch

Bulb (1.4 W)

Coolant level warning ECU

Bulb (3.4 W)

Fuel sender, gauge, Seat belt warning relay

Bulb (21 W)

Turn signal flasher relay

Dry cell battery

Fuel sender gauge

Heat light

Seat heater

Hexagon wrench (6 mm)

Power seat

BE–8

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BODY ELECTRICAL SYSTEM

Preparation