Lexus RX300 (MCU15). Service manual - part 318

N16045

3

4

DI–504

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300   (RM785E)

3

Check control switch.

PREPARATION:
(a)

Remove steering wheel center pad.

(b)

Disconnect the control switch connector.

CHECK:
Measure resistance between terminals 3 and 4 of control switch
connector when control switch is operated.

Switch position

Resistance (Ω)

Neutral

∞

 (No continuity)

RES/ACC

220 – 260

SET/COAST

610 – 650

CANCEL

1520 – 1560

NG

Replace control switch.

OK

4

Check harness and connector between cruise control ECU and cruise control switch,
cruise control switch and body ground (See page IN–32).

NG

Repair or replace harness or connector.

OK

5

Input signal check (See step 1).

OK

Wait and see.

NG

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

Input Signal

Indicator Light
Blinking Pattern

Stop Light 
switch ON

Light

OFF

ON

SW OFF

SW ON

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–505

LEXUS RX300   (RM785E)

Stop Light Switch Circuit

CIRCUIT DESCRIPTION

When the brake pedal is depressed, the stop light switch sends a signal to the ECU. When the ECU receives
this signal, it cancels the cruise control. A fail–safe function is provided so that the cancel functions normally,
even if there is a malfunction in the stop light signal circuit. The cancel conditions are: Battery positive voltage
at terminal STP–. When the brake is ON, battery positive voltage normally is applied through the STOP fuse
and stop light switch to terminal STP– of the ECU, and the ECU turns the cruise control OFF.
If the harness connected to terminal STP– has an open circuit, terminal STP– will have battery positive volt-
age and the cruise control will be turned OFF.
Also, when the brake is ON, the magnetic clutch circuit  is cut mechanically by the stop light switch, turning
the cruise control OFF. (See page DI–486 for operation of the magnetic clutch)

WIRING DIAGRAM

Refer to DTC 12 on page DI–486.

INSPECTION PROCEDURE

1

Check operation of stop light.

CHECK:
Check that stop light comes ON when brake pedal is depressed, and turns OFF when brake pedal is re-
leased.

NG

Check stop light system (See page BE–2).

OK

2

Input signal check.

CHECK:
(a)

See input signal check on DI–474.

(b)

Check the indicator light when the brake pedal is de-
pressed.

OK:

The indicator light goes OFF when the brake pedal is
depressed.

OK

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

NG

DI84W–01

I16972

ON

STP–

(–)

(+)

DI–506

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300   (RM785E)

3

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

PREPARATION:
(a)

Remove the ECU with connectors still connected.

(b)

Turn ignition switch ON.

CHECK:
Measure voltage between terminal STP– of cruise control ECU
connector and body ground, when the brake pedal is de-
pressed and released.
OK:

Depressed

10 – 14 V

Released

Below 1 V

OK

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

NG

4

Check for open in harness and connectors between terminal STP– of cruise con-
trol ECU and stop light switch (See page IN–32).

NG

Repair or replace harness or connector.

OK

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

F03293

Cruise Control ECU

C16

4

D

Skid Control ECU

CCS

21

A23

G–B

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–507

LEXUS RX300   (RM785E)

Neutral Start Switch Circuit

CIRCUIT DESCRIPTION

When the shift position is except D, a signal is sent from the neutral start switch to the ECU. When this signal
is input during cruise control driving, the ECU cancels the cruise control.

WIRING DIAGRAM

DI08V–23