Mitsubishi 380. Manual - part 66

SYMPTOM PROCEDURES

SIMPLIFIED WIRING SYSTEM (SWS)

54B-261

STEP 1. Use Diagnostic Tool MB991958 to select "ECU 
COMM Check" on the SWS monitor display. 
Check the following ECUs:

• Column switch (column-ECU)

• Front-ECU

CAUTION

To prevent damage to Diagnostic Tool MB991958, always 
turn the ignition switch to the "LOCK" (OFF) position 
before connecting or disconnecting Diagnostic Tool 
MB991958. Connect special tool MB991910 before con-
necting special tool MB991812. Be sure to connect special 
tool MB991806 after turning on special tool MB991824.
(1) Connect the special tool. Refer to "How to connect SWS 

monitor 

P.54B-13

."

(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Operate Diagnostic Tool MB991958 according to the 

procedure below to display "ECU COMM Check."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "ECU COMM Check."

(4) Diagnostic Tool MB991958 should show "OK" on the "ECU 

COMM Check" menus for both the "COLUMN ECU" and 
the "FRONT ECU" menus.

Q: Is "OK" displayed for both the "COLUMN ECU" and 

"FRONT ECU" menu?
"OK" is displayed for all the items : Go to Step 2.
"NG" is displayed for the "COLUMN ECU" menu : Refer 

to Inspection Procedure A-2 "Communication with the 
column switch (column-ECU) is not possible 

P.54B-68

."

"NG" is displayed for the "FRONT ECU" menu : Refer to 

Inspection Procedure A-4 "Communication with the 
front-ECU is not possible 

P.54B-80

."

00DB076A

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC302210

COLUMN SWITCH 
CONNECTOR

COLUMN SWITCH 
CONNECTOR AT 
HARNESS SIDE 

MB991812

AB

SYMPTOM PROCEDURES

SIMPLIFIED WIRING SYSTEM (SWS)

54B-262

STEP 2. Check the input signal by using "FUNCTION 
DIAG." menu of the SWS monitor.
Check the input signals from the following switches:

• Ignition switch: ON

• Lighting switch: TAIL

NOTE: Turn the ignition switch to the "ON" position in order to 
disable the headlamp automatic shutdown function.
(1) Operate Diagnostic Tool MB991958 according to the 

procedure below to display "TAILLAMP."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "Function Diag."
f.

Select "LIGHTING."

g. Select "TAILLAMP."

(2) Check that normal conditions are displayed for the items 

described in the table below.

Q: Does the Diagnostic Tool MB991958 display the items 

"TAILLAMP SW", "H/L AUTO-CUT" and "FRONT ECU 
ACK" as normal condition?
Normal conditions are displayed for all the items : Go to 

Step 3.

Normal condition is not displayed for "TAILLAMP SW" : 

Refer to Inspection Procedure M-5 "ETACS-ECU 
does not receive any signal from the taillamp switch 

P.54B-420

."

Normal condition is not displayed for "H/L AUTO-CUT" : 

Refer to Inspection Procedure H-9 "Headlamp 
automatic shutoff function does not work normally 

P.54B-305

."

Normal condition is not displayed for "FRONT ECU 
ACK" : Replace the front-ECU. Verify that the taillamps 

illuminate normally.

ITEM NO.

ITEM NAME

NORMAL CONDITION

ITEM 01

TAILLAMP SW

ON

ITEM 35

H/L AUTO-CUT

OFF

ITEM 70

FRONT ECU ACK

NORMAL ACK

00DB076A

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC302210

COLUMN SWITCH 
CONNECTOR

COLUMN SWITCH 
CONNECTOR AT 
HARNESS SIDE 

MB991812

AB

SYMPTOM PROCEDURES

SIMPLIFIED WIRING SYSTEM (SWS)

54B-263

STEP 3. Check front-ECU connector A-11X for loose, 
corroded or damaged terminals, or terminals pushed back 
in the connector.
Q: Is front-ECU connector A-11X in good condition?

YES : Go to Step 4.
NO :  Repair or replace the damaged component(s). Refer 

to GROUP 00E, Harness Connector Inspection 

P.00E-2

. Verify that the taillamps illuminate normally.

STEP 4. Check the battery power supply circuit to the 
front-ECU. Measure the voltage at front-ECU connector 
A-11X.
(1) Disconnect front-ECU connector A-11X and measure the 

voltage available at the relay box side of the connector.

(2) Measure the voltage between terminal 7 and ground.

• The voltage should measure approximately 12 volts 

(battery positive voltage).

Q: Is the measured voltage approximately 12 volts (battery 

positive voltage)?
YES : Replace the front-ECU. Verify that the taillamps 

illuminate normally.

NO :  Go to Step 5.

AC305977AH

CONNECTOR: A-11X

RELAY BOX SIDE 

AC305977AH

CONNECTOR: A-11X

RELAY BOX SIDE 

5

11

9

10

8 7 6

2

4 3

1

AC209867AB

CONNECTOR A-11X
(RELAY BOX SIDE)

SYMPTOM PROCEDURES

SIMPLIFIED WIRING SYSTEM (SWS)

54B-264

STEP 5. Check the wiring harness between front-ECU 
connector A-11X (terminal 7) and the battery.
Q: Is the wiring harness between front-ECU connector 

A-11X (terminal 7) and the battery in good condition?
YES : No action is necessary and testing is complete.
NO :  The wiring harness may be damaged or the 

connector(s) may have loose, corroded or damaged 
terminals, or terminals pushed back in the connector. 
Repair the wiring harness as necessary. Verify that 
the taillamps illuminate normally.

INSPECTION PROCEDURE H-2: Headlamp and Taillamp: The headlamps (low-beam) do not illuminate 
normally.

NOTE: This troubleshooting procedure requires the 
use of Diagnostic Tool MB991958 and SWS monitor 
kit MB991813. For details on how to use the SWS 
monitor, refer to "How to connect SWS monitor 

P.54B-13

."

.

CIRCUIT OPERATION

• When the lighting switch is set to "HEAD" posi-

tion, the "HEAD" signal is sent through the col-
umn-ECU (incorporated in the column switch) to 
the front-ECU. If the front-ECU receives the 
"HEAD" signal through the column-ECU, the 
front-ECU turns on the headlamp relay (incorpo-
rated in the front-ECU), thus causing the 
headlamps to illuminate. The headlamps always 
illuminate at low-beam by the headlamp dimmer 
switch automatic resetting function.

• If the SWS communication line is defective, the 

front-ECU operates the headlamps by using the 
other communication lines (headlamp backup cir-
cuit) instead of that line.

.

TECHNICAL DESCRIPTION (COMMENT)

If the headlamps (low-beam) do not illuminate nor-
mally, the column switch or the front-ECU may be 
defective.

.

TROUBLESHOOTING HINTS

• Refer to circuit diagrams GROUP-

90

• Refer to configuration diagrams GROUP-

80

• Trouble in input signal system

• The wiring harness or connectors may have 

loose, corroded, or damaged terminals, or termi-
nals pushed back in the connector

• The front-ECU may be defective

DIAGNOSIS

Required Special Tools:

• MB991223: Harness Set

• MB991958: Diagnostic Tool (MUT-III Sub Assembly)

• MB991824: Vehicle Communication Interface (V.C.I.)

• MB991827: MUT-III USB Cable

AC305977AH

CONNECTOR: A-11X

RELAY BOX SIDE 

AC305977AE

CONNECTOR: A-11X