Lexus RX300 (MCU15). Service manual - part 362

DI2AV–09

I19180

Body ECU

Driver Door
ECU

Sliding Roof
ECU

Engine & ECT ECU

Passenger Door
Door

Rear Right Door
ECU

Center Cluster
Integration Panel

Rear Left
Door ECU

A/C and Combination
Meter Integrated
ECU

Theft Deterrent
ECU

Double Lock 
Control Relay

DI–678

–

DIAGNOSTICS

MULTIPLEX COMMUNICATION SYSTEM

LEXUS RX300   (RM785E)

PRE–CHECK

1.

DIAGNOSIS SYSTEM

(a)

As shown in the following illustration, each ECU of this ve-
hicle is connected by communication bus and it transmits
each signal by communication. This communication bus
is self–diagnosed by Body No.1 ECU and it memorizes
DTC when it detects communication stop to ECU or com-
munication bus +B short or GND short. There is a possibil-
ity that Body No.1 ECU cannot self–diagnose accurately
unless it doesn’t work normal. So, please note that the
troubleshooting  of Body Electrical System should be
done after confirming if Body No.1 ECU and Open door
indicator works normal by 2 ”BASIC INSPECTION” de-
scribed later.

I03343
I03344
I03345

I03977

ECU

ECU

ECU

ECU

ECU

ECU

Open

Open

ECU

ECU

Open

ECU

Disconnection (DTC is detected)

Open (DTC is detected)

Open (DTC is not detected)

I03346

Body ECU

Open

Open

Detect the DTC of commu-
nication stop of the 3 ECUs.

Example

–

DIAGNOSTICS

MULTIPLEX COMMUNICATION SYSTEM

DI–679

LEXUS RX300   (RM785E)

(b)

If DTC of ECU communication stop is output, there is a
possibility of connector disconnection or 2 communica-
tion buses open. It will not become abnormal with only 1
communication bus open.

(c)

If 2 communication buses are open at the position as
shown in the illustration, DTC of ECU communication stop
between those 2 buses is output.

DI–680

–

DIAGNOSTICS

MULTIPLEX COMMUNICATION SYSTEM

LEXUS RX300   (RM785E)

2.

BASIC INSPECTION

INSPECT BODY ECU

1

Check Body ECU operation.

HINT:
With this inspection Body ECU CPU can be diagnosed if it works normal or not.
CHECK:
Check if the luggage compartment door opener works normal.

OK

Go to next step”OPEN DOOR INDICATOR LIGHT
INSPECTION”.

NG

Repair of replace malfunction part.

I07376

N09214

TC CG

–

DIAGNOSTICS

MULTIPLEX COMMUNICATION SYSTEM

DI–681

LEXUS RX300   (RM785E)

INSPECT OPEN DOOR INDICATOR LIGHT.

1

Check open door indicator light.

CHECK:
Check if open door Indicator light is turned on when either door
open.
HINT:
If open door Indicator light is not turned on, DTC will not be out-
put.

NG

Repair the open door indicator light (See page
BE–68).

OK

”Check DTC”

3.

DTC CHECK (Using diagnosis check wire)

(a)

Using SST, connect terminals 13 (TC) and 4 (CG) of
DLC3.
SST

09843–18040

(b)

Turn the ignition switch ON.

(c)

Read the DTC on the open door indicator light.