Lexus RX300 (MCU15). Service manual - part 315

I00051

ABS Speed Sensor

ABS ECU

Combination
Meter

Cruise Control ECU

DI–492

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300   (RM785E)

DTC

21

Open in Vehicle Speed Sensor Circuit

CIRCUIT DESCRIPTION

The vehicle speed sensor circuit is sent to cruise control ECU as vehicle speed signal. For each rotation of
the shaft, the vehicle speed sensor sends a signal through the combination meter to the cruise control ECU
(See the following chart). The ECU calculates the vehicle speed from this pulse frequency.

DTC No.

Detection Item

Trouble Area

21

Speed signal is not input to the cruise control ECU while cruise

control is set.

S

Combination meter

S

Harness or connector between cruise control ECU and com-

bination meter, combination meter and vehicle speed sensor

S

Vehicle speed sensor

S

Cruise control  ECU

DI08P–25

I19251

Cruise Control ECU

12

V–W

V–W

J/B No. 3

Combination Meter ECU

3K

3E

C16

12

2

SPD

IJ1

8

V–W

R–B

C12

10

C10

20

IE2

7

R–B

A23

16

Skid Control ECU

SP1

Input Signal

Indicator Light
Blinking Pattern

Drive at about 
40 km/h (25 mph)
or below

Drive at about 
40 km/h (25 mph)
or higher

Light ON

OFF

Light

ON

OFF

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–493

LEXUS RX300   (RM785E)

WIRING DIAGRAM

INSPECTION PROCEDURE

1

Input signal check.

CHECK:
(a)

See input signal check on page DI–474.

(b)

Check indicator light operation when driving with vehicle
speed above 40 km/h (25 mph), and with vehicle speed
below 40 km/h (25 mph).

OK:

Vehicle speed above 40 km/h (25 mph): 
                                               Indicator light blinks
Vehicle speed below 40 km/h (25 mph):
                                               Indicator light stays on

OK

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

NG

DI–494

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300   (RM785E)

2

Check speedometer circuit (See Combination meter troubleshooting on page 
BE–62).

NG

Repair or replace harness, connector or com-
bination meter assembly.

OK

3

Check harness and connector between cruise control ECU and combination me-
ter, combination meter and vehicle speed sensor (See page IN–32).

NG

Repair or replace harness or connector.

OK

4

Check vehicle speed sensor (See page BE–68).

NG

Replace vehicle speed sensor.

OK

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

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–495

LEXUS RX300   (RM785E)

DTC

23

Vehicle Speed Signal Abnormal

CIRCUIT DESCRIPTION

See page DI–492.

DTC No.

Detection Item

Trouble Area

23

Vehicle speed sensor pulse is abnormal.

S

Vehicle speed sensor

S

Cruise control ECU

WIRING DIAGRAM

See page DI–492.

INSPECTION PROCEDURE

1

Check vehicle speed sensor (See page BE–68).

NG

Replace vehicle speed sensor.

OK

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

DI08Q–16