Lexus ES300 (1997 year). Manual - part 435

N21224

Cruise Control ECU

1

B

Junction
Connector

B

W–R

10

1V

3

1W

W–R

2J

7

ECU–B

Engine Room J/B

1

2A

B

1

FL BLOCK

1

B–G

FL MAIN

Battery

J3

Instrument Panel J/B

F6

F8

W–R

BATT

C14

Short Pin

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–517

669

1997 LEXUS ES300   (RM511U)

Back–up Power Source Circuit

CIRCUIT DESCRIPTION

The ECU back–up power source provides power even when the ignition is off and is used for DTC memory,
etc..

WIRING DIAGRAM

DI0F8–01

N20674

ECU–B
Fuse

Engine Room Junction Block No.2

N19924

BATT

(–)

(+)

DI–518

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

670

1997 LEXUS ES300   (RM511U)

INSPECTION PROCEDURE

1

Check ECU–B fuse.

PREPARATION:
Remove the ECU–B fuse from engine room junction block
No.2.
CHECK:
Check continuity of ECU–B fuse.
OK:

Continuity

NG

Check for short in all the harness and compo-
nents connected to the ECU–B fuse.

OK

2

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

PREPARATION:
Remove the ECU with connector still connected.
CHECK:
Measure voltage between terminal BATT of ECU connector
and body ground.
OK:

Voltage: 10 – 14 V

OK

Proceed to next circuit inspection shown on
problem symptom table (See page 

DI–487

).

NG

Check and repair harness and connector be-
tween battery and cruise control ECU 
(See page 

IN–27

).

AB0119
N19925

I00745

ON

CMS

(–)

(+)

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

DI–519

671

1997 LEXUS ES300   (RM511U)

Main Switch Circuit (Cruise Control Switch)

CIRCUIT DESCRIPTION

When the cruise control main switch is turned off, the cruise control does not operate.

WIRING DIAGRAM

See page 

DI–499

.

INSPECTION PROCEDURE

1

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

PREPARATION:
(a)

Remove the ECU with connector still connected.

(b)

Turn ignition switch ON.

CHECK:
Measure voltage between terminal CMS of cruise control ECU
connector when main switch is held on and off.
OK:

Main switch

Voltage

OFF

10 – 14 V

ON

Below 0.5 V

OK

Proceed to next circuit inspection shown on
problem symptom table (See page 

DI–487

).

NG

DI0FA–01

N15969

3

5

DI–520

–

DIAGNOSTICS

CRUISE CONTROL SYSTEM

672

1997 LEXUS ES300   (RM511U)

2

Check main switch continuity.

PREPARATION:
(a)

Remove steering wheel center pad 
(See page 

SR–11

).

(b)

Disconnect the control switch connector.

CHECK:
Check continuity between terminals 3 and 5 of control switch
connector when main switch is held on and off.
OK:

Switch position

Tester connection

Specified condition

OFF

3 – 5

No continuity

Hold ON

3 – 5

Continuity

NG

Replace control switch.

OK

3

Check harness and connector between cruise control ECU and main switch 
(See page 

IN–27

).

NG

Repair or replace harness or connector.

OK

Check and replace cruise control ECU 
(See page 

IN–27

).