Lexus RX300 (MCU15). Service manual - part 396

DI3FU–02

I08282

A18 
Room Temp.
Sensor

1

2

G–W

SG–3

TR

A/C ECU
(Combination meter ECU)

G–R

9

3

C11

C11

DI–814

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

CIRCUIT INSPECTION

DTC

B1411/11 Room Temperature Sensor Circuit

CIRCUIT DESCRIPTION

This sensor detects the temperature inside the cabin and sends the appropriate signals to the A/C ECU
(Combination meter ECU).

DTC No.

Detection Item

Trouble Area

B1411/11

Open or short in room temperature sensor circuit.

S Room temperature sensor.

S Harness or connector between room temperature sensor and

A/C ECU (Combination meter ECU).

S A/C ECU (Combination meter ECU).

WIRING DIAGRAM

I08329

TR

SG–3

(+)

(–)

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–815

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

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

1

Check room temp. sensor using hard– held tester.

PREPARATION:
Connect the hard–held tester to the DLC3.
CHECK:
Check the room temp. sensor using DATA LIST.

OK

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

NG

2

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

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

Turn ignition switch ON.

(b)

Measure voltage between terminals TR and SG–3 of A/C
ECU (Combination meter ECU) connector at each tem-
perature.

OK:

Voltage :
at 25

°C (77°F) : 1.8 – 2.2 V

at 40

°C (104°F) : 1.2 – 1.6 V

HINT:
As the temperature increases, the voltage decreases.

NG

Go to step 3.

OK

Proceed to next circuit inspection shown on problem symptoms table (See page DI–812).  Howev-
er, if DTC B1411/11 is displayed, check and replace A/C ECU (Combination meter ECU).

I08330

2

1

DI–816

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

3

Check room temperature sensor.

PREPARATION:
Disconnect room temperature sensor connector.
CHECK:
Measure resistance between terminals 1 and 2 of room temper-
ature sensor connector at each temperature.
OK:

Resistance :
at 25

°C (77°F) : 1.61 – 1.78 kΩ

at 50

°C (122°F) : 0.55 – 0.65 kΩ

HINT:
As the temperature increases, the resistance decreases.

NG

Replace room temperature sensor.

OK

4

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

NG

Repair or replace harness or connector.

OK

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

I08331

A1 
Ambient
Temp. Sensor

2

1

TAM

A/C ECU
(Combination meter ECU)

C12

7

B–R

IJ1

12

EC1

11

EC1

17

IJ1

13

W–R

W–R

W–R

B–R

B–R

SG–5

16

C12

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–817

LEXUS RX300   (RM785E)

DTC

B1412/12 Ambient Temperature Sensor Circuit

CIRCUIT DESCRIPTION

This sensor detects the ambient temperature and sends the appropriate signals to the A/C ECU (Combina-
tion meter ECU).

DTC No.

Detection Item

Trouble Area

B1412/12

Open or short in ambient temperature sensor circuit.

S Ambient temperature sensor.

S Harness or connector between ambient temperature sensor

and A/C ECU (Combination meter ECU)

S A/C ECU (Combination meter ECU)

WIRING DIAGRAM

DI3FV–03