Lexus RX300 (MCU15). Service manual — part 398

N16207

Thermometer

Ice

More than
10 cm (3.94in.)

DI–822

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300 (RM785E)

3

Check evaporator temperature sensor.

PREPARATION:
Remove evaporator temperature sensor (See page AC–67).
CHECK:
Measure resistance between terminals 1 and 2 of evaporator
temperature sensor connector at each temperature.
OK:

Resistance :
at 0

°C (32°F) : 4.5 – 5.2 kΩ

at 15

°C (59°F) : 2.0 – 2.7 kΩ

HINT:
As the temperature increases, the resistance decreases.

NG

Replace evaporator temperature sensor.

OK

4

Check harness and connector between A/C ECU (Combination meter ECU) and
evaporator temperature sensor (See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace A/C ECU (Combination
meter ECU).

Resistance of photodiode

High

Low

Weak

Strong

Strength of solar radiation

I08369

Solar Sensor

A/C ECU (Combina-
tion meter ECU)

1

2

Y–B

L

C11

15

TS

S5–3

16

C11

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–823

LEXUS RX300 (RM785E)

DTC

B1421/21 Solar Sensor Circuit

CIRCUIT DESCRIPTION

A photo diode in the solar sensor detects solar radiation and
sends signals to the A/C ECU (Combination meter ECU).

DTC No.

Detection Item

Trouble Area

B1421/21

Open or short in solar sensor circuit.

Please note that display of diagnostic trouble code 21 is not

abnormal when the sensor is not receiving solar radiation.

S Solar sensor.

S Harness or connector between solar sensor and A/C ECU

(Combination meter ECU).

S A/C ECU (Combination meter ECU).

WIRING DIAGRAM

DI3FX–02

I08337

TS

S5–3

(+)

(–)

DI–824

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300 (RM785E)

INSPECTION PROCEDURE

HINT:
In case of using the hand–held tester, start the inspection step 1 and in case of not using the hand–held
tester, start from step 2.

1

Check solar sensor using hand–held tester.

PREPARATION:
Connect the hand–held tester to the DLC3.
CHECK:
Check the solar sensor using DATA LIST.

OK

Check and replace A/C ECU (Combination me-
ter ECU).

NG

2

Check voltage between terminals TS and S5–3 of A/C ECU (Combination meter
ECU) connector.

PREPARATION:
Remove A/C ECU with connectors still connected.
CHECK:
(a)

Turn ignition switch ON.

(b)

Measure voltage between terminals TS and S5–3 of A/C
ECU connector when the solar sensor is subjected to an
electric light, and when the sensor is covered by al cloth.

OK:

Condition

Voltage

Sensor subjected to electric light

0.8 – 4.3 V

Sensor covered by a cloth

Below 0.8 V

HINT:
As the inspection light is moved away from the sensor, the volt-
age increases.

NG

go to step 3.

OK

Proceed to next circuit inspection shown on problem symptoms table (See page DI–812). Howev-
er, if DTC B1421/21 is displayed, check and replace A/C ECU (Combination meter ECU).

I08357

2

1

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–825

LEXUS RX300 (RM785E)

3

Check solar sensor.

PREPARATION:
Remove solar sensor.
CHECK:
(a)

Cover the sensor by a cloth.

(b)

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

HINT:
Connect positive (+) lead of ohmmeter to terminal 1 and nega-
tive (–) lead to terminal 2 of the solar sensor.
OK:

Resistance : ∞ Ω (no continuity)

PREPARATION:
(a)

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

(b)

Measure resistance.

OK:

Resistance : Approx. 4 kΩ (continuity)

HINT:
As the electric light is moved away from the sensor, the resis-
tance increases.

NG

Replace solar sensor.

OK

4

Check harness and connector between A/C ECU (Combination meter ECU) and
solar sensor (See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace A/C ECU (Combination
meter ECU).