Lexus RX300 (MCU15). Service manual - part 226

DI–136

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

NG

2

Check for open in harness and connector between engine ECU and starter relay
(See page IN–32).

NG

Repair or replace harness or connector.

OK

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

A14524

Check Engine
Warning Light

Engine ECU

Instrument Panel J/B

W

Battery

E9

6

IG1

C12

C10

HEATER

Y–G

1

F11

8

J/B No. 3

Ignition Switch

19

2

13

B–Y

7

1

1

ALT

AM1

R–W

4

FL Block

3A

3E

1A

6

5

AM1

W–L

IE2

Y–G

W

1C

1C

1K

R–W

I15

–

DIAGNOSTICS

ENGINE

DI–137

LEXUS RX300   (RM785E)

Check Engine Warning Light Circuit Malfunction

CIRCUIT DESCRIPTION

If the engine ECU detects trouble, the check engine warning lights up. At this time, the engine ECU records
a DTC in memory.

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:
Troubleshoot in accordance with the chart below for each trouble symptom.

Check engine does not light up

Start inspection from step 1 in case of using hand–held tester and

start from step 2 in case of not using hand–held tester

Check engine remains on

After inspection of step 3, start inspection from step 4 in case of

using hand–held tester and start from step 5 in case of not using

hand–held tester

DI6QO–07

DI–138

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

1

Check operation of check engine warning light.

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

Turn the ignition switch ON and push the hand–held tester main switch ON.

(c)

Switch the hand–held tester from the normal mode to the check mode.

CHECK:
Check if the check engine warning light blinks.
OK:

The check engine warning light blinks.

OK

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

NG

2

Check check engine warning light.

See combination meter troubleshooting (See page BE–2).

NG

Repair or replace bulb or combination meter as-
sembly.

OK

3

Check that engine ECU connectors are securely connected to engine ECU.

NO

Connect connector to engine ECU.

YES

Check for open circuit in harness and connector between combination meter and engine ECU
(See page IN–32).

–

DIAGNOSTICS

ENGINE

DI–139

LEXUS RX300   (RM785E)

4

Check operation of check engine warning light (See step 1).

OK

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

NG

5

Is DTC output?

Check DTC on page DI–3.

YES

Repair circuit indicated by output code.

NO

6

Check HEATER fuse.

OK

Check for short in all harness and components
connected to HEATER fuse.

NG

Check for short circuit in harness and connector between DLC3 and engine ECU (See page 
IN–32).