Lexus RX300 (MCU15). Manual — part 316

I16913

Cruise Control ECU

E9

Engine and ECT ECU

IDLO

IDL

25

13

B–Y

C16

DI–496

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300 (RM785E)

DTC

51

Idle Signal Circuit

CIRCUIT DESCRIPTION

When the idle switch is turned ON, a signal is sent to the ECU. The ECU uses this signal to correct the dis-
crepancy between the throttle valve position and the actuator position sensor value to enable accurate
cruise control at the set speed. If the idle switch is malfunctioning, problem symptoms also occur in the en-
gine, so also inspect the engine.

DTC No.

Detection Item

Trouble Area

51

Short in idle signal circuit.

S

Harness or connector between Engine and ECT ECU and

throttle position sensor

S

Harness on connector between cruise control ECU and En-

gine and ECT ECU

S

Cruise control ECU

WIRING DIAGRAM

DI3VK–06

I16971

ON

IDL

(–)

(+)

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–497

LEXUS RX300 (RM785E)

INSPECTION PROCEDURE

1

Check voltage between terminal IDL of cruise control ECU connector and body
ground.

PREPARATION:
(a)

Remove the ECU with connector still connected.

(b)

Disconnect the engine and ECT ECU connector.

(c)

Turn ignition switch ON.

CHECK:
Measure voltage between terminal IDL of ECU connector and
body ground when the throttle valve is fully closed and fully
opened.
OK:

Throttle valve position

Voltage

Fully opened

10 – 14 V

Fully closed

Below 1.5 V

OK

Proceed to next circuit inspection shown in
problem symptom table (See page DI–483).

NG

2

Check harness and connector between engine and ECT ECU and throttle posi-
tion sensor (See page IN–32).

NG

Repair or replace harness or connector.

OK

3

Check throttle position sensor circuit.

NG

Replace throttle position sensor.

OK

DI–498

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300 (RM785E)

4

Check for open and short in harness and connector between cruise control ECU
and engine and ECT ECU (See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace cruise control ECU (See
page IN–32).

I21177

Cruise Control ECU

2

B

B–R

D

D

Instrument Panel J/B

1G

1C

B–Y

4

Ignition Switch

2

AM1

1A

ALT

1C

W–L

Battery

16

GND

IE

W

1

6

B–R

J4
J/C

Instrument Panel J/B

C16

C16

ECU–IG

7

13

1

2

3

BR

AM1

IG1

W

FL BLOCK

5

BR

A

J5
J/C

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–499

LEXUS RX300 (RM785E)

ECU Power Source Circuit

CIRCUIT DESCRIPTION

The ECU power source supplies power to the actuator and sensors, etc, when terminal GND and the cruise
control ECU case are grounded.

WIRING DIAGRAM

DI08X–23