Lexus SC300 / Lexus SC400. Manual - part 23

Diag. Code 14

Water Temperature Sensor Circuit

CIRCUIT DESCRIPTION

This sensor detects the coolant temperature and sends the appropriate signals to the air conditioner
control assembly. These signals are used for warm up control when the engine is cold.

Code No.

Diag. Code Detecting Condition

Trouble area

14

Open or short in water temperature sensor
circuit.

Water temperature sensor.

Harness or connector between water 
temperature sensor and A/C control as-
sembly.

A/C control assembly.

DIAGNOSTIC CHART

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

Check water temperature sensor.

Check harness and connector between air

conditioner control assembly and water tem-
perature 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

14 is displayed, check and replace

air conditioner control assembly.

Replace water  temperature
sensor.

Repair or replace harness or
connector.

AC–50

–

AIR CONDITIONING SYSTEM

Troubleshooting

Check voltage between terminals TW 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.

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

Voltage

at 0

°

C (32

°

F) :   2.8~3.2 V

at 40

°

C (104

°

F) :   1.8~2.2 V

at 70

°

C (158

°

F) :   0.9~1.3 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 14 is displayed, check and
repair air conditioner control assembly.

Check water temperature sensor.

(1)

Remove heater unit.

(2)

Remove water temperature sensor.

Measure resistance between terminals 1 and 3 of
water  temperature sensor connector at each temper-
ature.

Resistance

at 0

°

C (32

°

F) :   16.5~17.5 k

at 40

°

C (104

°

F) :   2.4~2.8 k

at 70

°

C (158

°

F) :   0.7~1.0 k

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

Replace  water temperature sensor.

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

IN-27

).

Repair or replace harness or connector.

Check and replace air conditioner control
assembly.

INSPECTION PROCEDURE

–

AIR CONDITIONING SYSTEM

Troubleshooting

AC–51

Diag. Code 21

Solar Sensor Circuit

CIRCUIT DESCRIPTION

A photo diode in the solar sensor detects solar
radiation and sends signals to the air conditioner
control assembly.

Code No.

Diag. Code Detecting Condition

Trouble area

21

Open or short in solar sensor circuit. (Please
note that display of diagnostic code 21 is not
abnormal when the sensor is not receiving
solar radiation)

Solar sensor.

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

A/C control assembly.

DIAGNOSTIC CHART

Check voltage between terminals S5
and TS of air conditioner control as-
sembly connector.

Check solar sensor.

Check harness and connector between air

conditioner control assembly and solar sen-
sor (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

21 is displayed, check and replace

air conditioner control assembly.

Replace solar  sensor.

Repair or replace harness or
connector.

AC–52

–

AIR CONDITIONING SYSTEM

Troubleshooting

9

9

Check voltage between terminals S5 and TS of air conditioner
control assembly connector.

(1)

Remove console upper panel. (See page

 

BO-111

).

(2)

Remove A/C control assembly with connec-
tors still connected.

(3)

Turn ignition switch ON.
Measure voltage between terminals S5 and TS
of air conditioner control assembly connector
when the solar sensor is subjected to an electric
light, the sensor is covered by a cloth.

Condition

Voltage

Sensor subjected to electric light

Sensor covered by a cloth

Below 4 V

4 –4.5 V

In addition, when the inspection light is gradu-
ally moved away from the sensor,  the voltage
increases.

Proceed to next circuit inspection shown on

matrix chart (See page 

AC-36

).However,

when Diag. code 21 is displayed, check and
replace air conditioner control assembly.

Check  solar sensor.

(1)

Remove solar sensor from dashboard.

(2)

disconnect solar sensor connector.

Connect positive (+) lead of ohmmeter to terminal 2
and negative (–) lead to terminal 1 of the solar sensor.

(1)

Cover the sensor by a cloth.

(2)

Measure resistance between terminals 1 and
2 of solar sensor connector.

(1)

Remove the cloth from the solar sensor and
subject the sensor to electric light.

(2)

Measure resistance.

Resistance:

Approx, 4 k

 (continuity)

In addition, as the electric light is moved gradu-
ally away from the sensor the resistance in-
creases.

Replace solar sensor.

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

IN-27

).

Repair or replace harness or connector.

Check and replace air conditioner control
assembly.

INSPECTION PROCEDURE

–

AIR CONDITIONING SYSTEM

Troubleshooting

AC–53