Lexus RX300 (MCU15). Service manual - part 321

DI–516

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300   (RM785E)

Actuator Control Cable

INSPECTION PROCEDURE

1

Actuator control cable inspection

OK:
(a)

Check that the actuator and control cable throttle link are properly installed and that the cable and link
are connected correctly.

(b)

Check that the actuator and bell crank operate smoothly.

(c)

Check that the cable is not loose or too tight.

OK:

Freeplay: less than 10 mm

HINT:

S

If the control cable is very loose, the vehicle’s loss of speed going uphill will be large.

S

If the control cable is too tight, the idle RPM will become high.

DI092–09

I19253

Cruise Control ECU

OD

ECT

Engine and ECT ECU

S4

C16

1

12

6

14

R–Y

IH1

8

OD1

Y–G

E6

24

R

S4

E1 
ECT Solenoid

C16

E10

R–Y

R–Y

R–Y

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–517

LEXUS RX300   (RM785E)

Electronically Controlled Transmission Communication Circuit

CIRCUIT DESCRIPTION

When driving uphill under the cruise control, in order to reduce shifting due to ON–OFF overdrive operation
and to provide smooth driving, when down shifting in the electronically controlled transmission occurs, a sig-
nal to prevent upshift until the end of the uphill slope is sent from the cruise control ECU to the electronically
controlled transmission.
Terminal ECT of the cruise control ECU detects the shift change signal (output to electronically controlled
transmission No. 2 solenoid) from the engine and ECT ECU.
If the vehicle speeds down, also when terminal ECT of the cruise control ECU receives down shifting signal,
it sends a signal from terminal OD to ECM to cut overdrive until the end of the uphill slope, and the gear shifts
are reduced and gear shift points in the electronically controlled transmission are changed.

WIRING DIAGRAM

DI08U–23

I16973

ON

O/D

(–)

(+)

DI–518

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

1

Check operation of overdrive.

PREPARATION:
Test drive after engine warms up.
CHECK:
Check that overdrive ON ↔ OFF occurs by operation of OD switch ON–OFF.

NG

Check and repair electronically controlled
transmission (See page DI–142).

OK

2

Check voltage between terminal OD of harness side connector of cruise control
ECU and body ground.

PREPARATION:
(a)

Remove the ECU with connector still connected.

(b)

Turn ignition switch ON.

(c)

Disconnect the ECU connector.

CHECK:
Measure voltage between terminal OD of harness side connec-
tor of ECU and body ground.
OK:

Voltage: 10 – 14 V

NG

Go to step 5.

OK

I16974

ECT

(–)

(+)

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–519

LEXUS RX300   (RM785E)

3

Check voltage between terminal ECT of cruise control ECU connector and body
ground (On test drive).

PREPARATION:
(a)

Connect the ECU connector.

(b)

Test drive after engine warms up.

CHECK:
Check voltage between terminal ECT of ECU connector and
body ground when OD switch is ON and OFF.
OK:

OD switch position

Voltage

ON

8 – 14 V

OFF

Below 0.5 V

OK

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

NG

4

Check harness and connector between terminal ECT of cruise control ECU and
electronically controlled transmission solenoid (See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace cruise control ECU.

5

Check harness and connector between terminal OD of cruise control ECU and
terminal OD1 of 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).