Lexus SC300 / Lexus SC400. Service manual — part 22

Diag. Code 12

Ambient Temperature Sensor Circuit

CIRCUIT DESCRIPTION

This sensor detects the ambient temperature and sends the appropriate signals to the A/C control
assembly.

Code No.

Diag. Code Detecting Condition

Trouble area

12

Open or short in ambient temperature sensor
circuit.

Ambient temperature sensor.

Harness or connector between ambient
temperature sensor and A/C control assem-
bly.

A/C control assembly.

DIAGNOSTIC CHART

Check voltage between terminals TAM and
SG of air conditioner control assembly con-
nector.

Check ambient temperature sensor.

Check harness and connector between air

conditioner control assembly and ambient

temperature sensor. (See page

IN-27

).

Check and replace air conditioner control
assembly.

Proceed to next circuit inspection

shown on matrix chart (See

page

AC-36

). However, when Diag.

code 12 is displayed, check and re-

place air conditioner control assembly.

Replace ambient temperature
sensor.

Repair or replace harness or
connector.

AC–46

–

AIR CONDITIONING SYSTEM

Troubleshooting

Check voltage between terminals TAM and SG of air conditioner
control assembly connector.

(1)

Remove console upper panel. (See page

BO-111

(2)

Remove A/C control assembly with
connectors still connected.

(3)

Turn ignition switch ON.

Check voltage between terminals TAM and SG of air
conditioner control assembly connector at each tem-
perature.

at 25

°

C (77

°

F) : 1.35~1.75 V

at 40

°

C (104

°

F) : 0.85~1.25 V

In addition, as the temperature increases, the
voltage decreases gradually.

Proceed to next circuit inspection shown on
matrix chart (See page AC-36).However,
when Diag. code 11 is displayed, check and
replace air conditioner control assembly.

Check ambient temperature sensor.

(1)

Remove under cover

(2)

disconnect ambient temperature sensor
connector.

Check resistance between terminals 1 and 2 of
ambient temperature sensor connector at each
temperature.

Resistance

at 25

°

C (77

°

F) : 1.6~1.8k

at 50

°

C (122

°

F) : 0.5~0.7k

In addition, as the temperature increases, the
voltage decreases gradually.

Replace ambient temperature sensor.

Check for open and short in harness and connector between air conditioner
control assembly and ambient temperature sensor (See page

IN-27

).

Repair or replace harness or connector.

Check and repair air conditioner control
assembly.

Voltage

INSPECTION PROCEDURE

–

AIR CONDITIONING SYSTEM

Troubleshooting

AC–47

Diag. Code 13

Evaporator Temperature Sensor Circuit

CIRCUIT DESCRIPTION

This sensor detects the temperature inside the cooling unit and sends the appropriate signals to the air
conditioner control assembly.

Code No.

Diag. Code Detecting Condition

Trouble area

13

Open or short in evaporator temperature sensor
circuit.

Evaporator temperature sensor.

Harness or connector between evaporator
temperature sensor and A/C control
assembly.

A/C control assembly.

DIAGNOSTIC CHART

Check voltage between terminals TE
and SG of air conditioner control as-
sembly

Check evaporator temperature sensor.

Check harness and connector between air

conditioner control assembly and evapora-
tor temperature sensor (See page

IN-27

).

Check and replace air conditioner control
assembly.

10

Proceed to next circuit inspection

shown on matrix chart (See page

AC-36

). However, when Diag. code

13 is displayed, check and replace

air conditioner control assembly.

Replace evaporator temperature
sensor.

Repair or replace harness or
connector.

AC–48

–

AIR CONDITIONING SYSTEM

Troubleshooting

(1)

Remove console upper panel. (See page

BO–111

)

(2)

Remove A/C Control Assembly with connectors
still connected.

(3)

Turn ignition switch ON.

Measure voltage between terminals TE and SG of air
conditioner control assembly connector at each tem-
perature.

Voltage

at 0

°

C (32

°

F) : 2.0~2.4 V

at 15

°

C (59

°

F) : 1.4~1.8 V

In addition, as the temperature increases, the
voltage decreases gradually.

Proceed to next circuit inspection shown on
matrix chart (See page

AC-36

).However,

when Diag. code 11 is displayed, check and
replace air conditioner control assembly.

Check voltage between terminals TE and SG of air conditioner control

assembly connector.

Check evaporator temperature sensor.

Remove evaporator temperature sensor(See page

AC-124

).

Check resistance between terminals 1 and 2 of evap-
orator temperature sensor connector at each temper-
ature.

In addition, as the temperature increases, the
voltage decreases gradually.

Replace evaporator temperature sensor.

Check for open and short in harness and connector between air conditioner
control assembly and evaporator temperature sensor (See page

IN-27

).

Repair or replace harness or connector.

Check and replace air conditioner control
assembly.

Resistance

at 15

°

C (59

°

F) : 2.1~2.6k

at 0

°

C (32

°

F) : 4.6~5.1k

INSPECTION PROCEDURE

–

AIR CONDITIONING SYSTEM

Troubleshooting

AC–49