Lexus RX300 (MCU15). Service manual - part 400

I08341

PRE

(+)

(–)

ECM

Low Pressure Cut Side

Reference : High Pressure Cut Side

ON (0V)

196 kPa
OFF (12V)

225 kPa

ON (0V)

2,550 kPa

3,140 kPa

OFF (12V)

I07794

1

2

3

4

Low Pressure Cut Side

Reference : High Pressure Cut Side

ON (continuity)

OFF (continuity)

181 kPa

ON (continuity)

OFF (continuity)

211 kPa

3,140 kPa

2,550 kPa

DI–830

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

1

Check voltage between terminal PRE of engine and ECT ECU and body ground.

PREPARATION:
Install the manifold gauge set.
CHECK:
(a)

Turn ignition switch ON.

(b)

Check voltage between terminal PRE of engine and ECT
ECU connector and body ground when A/C gas pressure
is changed.

OK:

The voltage changes with gas pressure, as shown in
the diagram below.

OK

Proceed to next circuit inspection shown on
problem symptoms table (See page DI–812).

NG

2

Check pressure switch.

PREPARATION:
Disconnect pressure switch connector.
CHECK:
(a)

Turn ignition switch ON.

(b)

Check continuity between terminals 1 and 4 of pressure
switch when A/C gas pressure is changed.

OK:

The continuity changes with gas pressure as shown
below.

NG

Repair or replace harness or connector.

OK

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–831

LEXUS RX300   (RM785E)

3

Check harness and connector between engine and ECT ECU and pressure
switch, pressure switch and body ground (See page IN–32).

NG

Repair or replace harness or connector.

OK

4

Check harness and connector between engine and ECT ECU and A/C ECU (Com-
bination meter ECU). (See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace engine and ECT ECU.

4

(V)

1

TP

 terminal 

voltage

0

100 %

(Cool)

(Hot)

Damper opening angle

I08342

A25 
Air Mix Control Position Sensor
(Air Mix Control Servomotor)

1

5

3

3

9

6

IF1

G–R

B–R

R–L

3

7

10

S5–1

TP

SG–1

A/C ECU (Combina-
tion meter ECU)

C10

IF1

IF1

G–B

B–Y

B

C10

C10

DI–832

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

DTC

B1431/31 Air Mix Damper Position Sensor Circuit

CIRCUIT DESCRIPTION

This sensor detects the position of the air mix damper and
sends the appropriate signals to the A/C ECU (Combination
meter ECU).
The position sensor is built into the air mix damper control ser-
vomotor assembly.

DTC No.

Detection Item

Trouble Area

B1431/31

Short to ground or power source circuit in air mix damper posi-

S Air mix damper position sensor.

S Harness or connector between air mix damper control servo-

B1431/31

Short to ground or  ower source circuit in air mix dam er  osi

tion sensor circuit.

Harness or connector between air mix dam er control servo

motor assembly and A/C ECU (Combination meter ECU).

S A/C ECU (Combination meter ECU).

WIRING DIAGRAM

DI3G0–03

I08343

TP

SG–1

(–)

(+)

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–833

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

HINT:
In case of using the hand–held tester, start the inspection from step1 and in case of not using the hand–held
tester, start from step2.

1

Check air mix damper position using hand–held tester.

PREPARATION:
Connect the hand–held tester to the DLC3.
CHECK:
Check the current position of air mix damper and the target position of air mix damper (Passenger Side).
OK:

The current position and target position are almost similar.

OK

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

NG

2

Check voltage between terminals TP and SG–1 of A/C ECU (Combination meter
ECU) connector.

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

Turn ignition switch ON.

(b)

Change the set temperature to activate the air mix damp-
er control servomotor, and measure the voltage between
terminals TP and SG–1 of A/C ECU connector each time
when the set temperature is changed.

OK:

Set Temperature

Voltage

Max. cool

3.5 – 4.5 V

Max. hot

0.5 – 1.5 V

HINT:
As the set 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 B1431/31 displayed, check and replace A/C ECU (Combination meter ECU).