Lexus SC300 / Lexus SC400. Manual - part 144

2.

INSPECT MIRROR POSITION SENSORS
HINT: Strip off the vinyl tape of the connector and remove ter-
minals 1, 2, 3, 5 and 9 from the connector housing.
(a)  Connect a series of three 1.5 volt dry cell batteries.
(b)  Connect the positive (+) lead from the dry cell batteries

to terminal 5 and the negative (–) lead to terminal 9.

(c)  Connect the positive (+) lead from the voltmeter to

terminal 6 and the negative (–) lead to terminal 9.

(d)  Apply battery voltage to terminals 2 and 3, check that

the voltage gradually changes according to the table
below while the mirror moves between the uppermost
position and lowermost position.

Mirror

position

Lowermost

Uppermost

Voltage

2.8 – 5.0

Changes
gradually

0 – 0.9

If voltage value is not as specified, replace the motor assem-
bly.

(e)  Disconnect the four leads of the battery and voltmeter.
(f)  Connect the positive (+) lead from the voltmeter to

terminal 4 and the negative (–) lead to terminal 9.

(g)  Apply battery voltage to terminals 1 and 2n inspect that

the voltage gradually changes according to the table
below while the mirror moves between the leftmost
position and rightmost position.

Mirror

Position

Leftmost

Rightmost

Voltage

Left

Mirror

2.8 – 5.0

Changes
gradually

0 – 0.9

Voltage

Right

Mirror

0 – 0.9

Changes
gradually

2.8 – 5.0

If voltage value is not as specified, replace the motor assem-
bly.

(Mirror ECU)
REMOVAL AND INSTALLATION OF
MIRROR ECU

REMOVAL AND INSTALL MIRROR ECU

(a)  Remove the No. 1 under cover .

(See page 

BO–112

)

(b)  Remove the two screws and disconnect the two

connectors and then pull out the ECU.

(c)  For installation, follow the removal procedure in reverse.

–

BODY ELECTRICAL SYSTEM

Power Mirror Control System

BE–187

INSPECTION OF MIRROR ECU

1. 

INSPECT MIRROR ECU CIRCUIT
Disconnect the connectors from the ECU and inspect the
connector on the wire harness side as shown in the chart be-
low.

Check for

Tester connection

Condition

Specified value

Continuity

A1–A2

Constant

Continuity

A1–A3

Constant

Continuity

A8–A10

Constant

Continuity

A9–A10

Constant

Continuity

A11–Ground

Constant

Continuity

A12–A13

Constant

Continuity

A16–*

Constant

Continuity

B1–B2

Right mirror switch on DOWN

Continuity

B1–B4

Right mirror switch to RIGHT

Continuity

B1–B5

Left mirror switch to RIGHT

Continuity

B1–B6

Left mirror switch to DOWN

Continuity

B2–B3

Right mirror switch to UP

Continuity

B3–B4

Right mirror switch to LEFT

Continuity

B3–B5

Left mirror switch to LEFT

Continuity

B3–B6

Left mirror switch to UP

Continuity

Voltage

A4–Ground

Constant

Battery positive voltage

A7–Ground

Ignition switch to ACC

Battery positive voltage

A7–Ground

Ignition switch to OFF

No voltage

*: Terminal 1/18 of the Tilt and Telescopic ECU

If circuit is not as specified, inspect the wire harness and mir-
ror switch or motor assembly.

BE–188

–

BODY ELECTRICAL SYSTEM

Power Mirror Control System

2. 

INSPECT MIRROR ECU OPERATION
Connect the connectors and using a voltmeter with high im-
pedance (10 k

/V minimum), measure the voltage at each

terminal and body ground.

Check for

Tester connection

Condition

Specified value

Voltage

A1–Ground

Right mirror switch to LEFT

Battery positive voltage

A2–Ground

Right mirror switch to UP

Battery positive voltage

A3–Ground

Right mirror switch to RIGHT or DOWN

Battery positive voltage

*A5–Ground

Right mirror to leftmost position

0–0.9 V

*A5–Ground

Right mirror to rightmost position

2.8–5.0 V

*A6–Ground

Right mirror to lowermost position

2.8–5.0 V

*A6–Ground

Right mirror to uppermost position

0–0.9 V

A8–Ground

Left mirror switch to RIGHT

Battery positive voltage

A9–Ground

Left mirror switch to UP

Battery positive voltage

A10–Ground

Left mirror switch to LEFT or DOWN

Battery positive voltage

A13–Ground

Right or left mirror switch to any position except
OFF

Approx. 5 V

*A14–Ground

Left mirror to leftmost position

2.8–5.0 V

*A14–Ground

Left mirror to rightmost position

0–0.9 V

*A15–Ground

Left mirror to lowermost position

2.8–5.0 V

*A15–Ground

Left mirror to uppermost position

0–0.9 V

B2–Ground

Constant

Approx. 5 V

B4–Ground

Constant

Approx. 5 V

B5–Ground

Constant

Approx. 5 V

B6–Ground

Constant

Approx. 5 V

*: Confirm that the voltage changes gradually while the mirror moves

If operation is not as specified, inspect the wire harness and
mirror switch or motor assembly. Then if these are correct, re-
place the ECU.

–

BODY ELECTRICAL SYSTEM

Power Mirror Control System

BE–189

Troubleshooting

You will find the cause of trouble more easily by properly using the table shown below. In this table, the
numbers indicate the order of priority of the causes of trouble. Check each part in the order shown. If neces-
sary, replace the part.

See page

BE–4

,20

BE–4

,21

BE–186

BE–186

    –

–

BE–188

SR–60

    –

–

IN–32

BE–187

Trouble

Parts

name

RADIO NO. 2 Fuse

DOME Fuse

Mirror Switch

Mirror Motor

Wire Harness

Mirror ECU

Driving Position Switch

Driving Position Switch

(Position is not set)

T

ilt and T

elescopic 

ECU

Mirror Sensors

Mirror does not operate.

1

1

2

3

5

4

Mirror operates abnormally

1

2

4

3

Mirror does not return to the memorized position.
(w/ Memory System)

6

4

2

1

3

5

Mirror returns to a position which is not memorized.
(w/ Memory System)

3

1

2

BE–190

–

BODY ELECTRICAL SYSTEM

Power Mirror Control System