Mitsubishi 380. Manual - part 739

DIAGNOSIS

CONTROLLER AREA NETWORK (CAN)

54C-367

DIAGNOSTIC ITEM 9: Diagnose the lines between CAN main bus line and the ENGINE-ECU

NOTE: When diagnosing CAN-BUS on vehi-

cles with manual transmission (M/T), disregard 
A/T-ECU and it’s wiring circuits and measure 
between ABS-ECU and ENGINE-ECU only.

NOTE: When diagnosing CAN-BUS on vehicles 
not equipped with a multi-centre display, disre-
gard the multi-centre display and it’s wiring cir-
cuits.

CAUTION

When servicing a CAN bus line, ground yourself 
by touching a metal object such as an unpainted 
water pipe. If you fail to do so, a component con-
nected to the CAN bus line may be damaged.

.

TROUBLE JUDGMENT

If the MUT-III cannot receive signals from the 
ENGINE-ECU, CAN bus line connector(s) are bro-
ken or an open circuit has occurred.

.

COMMENTS ON TROUBLE SYMPTOM

The wiring harness wire or connectors may have 
loose, corroded, or damage terminals, or terminals 
pushed back in the connector, or the ENGINE-ECU 
may be defective.

.

TROUBLESHOOTING HINTS

• Refer to circuit diagrams GROUP-

90

• Refer to configuration diagrams GROUP-

80

• The wiring harness or connectors may have 

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

• The ENGINE-ECU may be defective

• The A/T-ECU may be defective

NOTE: When diagnosing CAN-BUS on vehi-

cles with manual transmission (M/T), disregard 
A/T-ECU and it’s wiring circuits and measure 
between ABS-ECU and ENGINE-ECU only.

16DB400A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER

16DB480A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER

A/T

CONTROL

UNIT

DIAGNOSIS

CONTROLLER AREA NETWORK (CAN)

54C-368

DIAGNOSIS

Required Special Tools:

• MB991223: Harness Set

• MB991219: Inspection Test Harness

• MB992044: ENGINE-ECU Harness

• MB992045: A/T-ECU Harness

STEP 1. Check  A/T-ECU connector B-19 and ENGINE-ECU 
connector B-21 for loose, corroded or damaged terminals, 
or terminals pushed back in the connector.

NOTE: when diagnosing CAN-BUS on vehicles with 
manual transmission (M/T), disregard A/T-ECU and it’s wir-
ing circuits and check between ABS-ECU and 
ENGINE-ECU only.

CAUTION

The strand end of the twisted wire should be within 10 cm 
(4 inches) from the connector. For details refer to 

P.54C-4

.

Q: Are A/T-ECU connector B-19 and ENGINE-ECU 

connector B-21 in good condition? 
YES : Go to Step 2.
NO :  Repair the damaged parts.

16DB400A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER

16DB480A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER

A/T

CONTROL

UNIT

DIAGNOSIS

CONTROLLER AREA NETWORK (CAN)

54C-369

STEP 2. Check the CAN bus lines between the 
ENGINE-ECU and the A/T-ECU. Measure the resistance 
between ENGINE-ECU connector B-21 and A/T-ECU 
connector B-19.

NOTE: when diagnosing CAN-BUS on vehicles with 
manual transmission (M/T), disregard A/T-ECU and it’s wir-
ing circuits and check between ABS-ECU and 
ENGINE-ECU only.

CAUTION

A digital multimeter should be used. For details refer to 

P.54C-4

.

CAUTION

The test wiring harness should be used. For details refer to 

P.54C-4

.

(1) Disconnect ENGINE-ECU connector B-21 and A/T-ECU 

connector B-19, and measure the resistance between each 
wiring harness side connector.

(2) Turn the ignition switch to the "LOCK" (OFF) position.

CAUTION

Disconnect the negative battery terminal. For details refer 
to 

P.54C-4

.

(3) Disconnect the negative battery terminal.

16DB400A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER

16DB480A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER

A/T

CONTROL

UNIT

DIAGNOSIS

CONTROLLER AREA NETWORK (CAN)

54C-370

(4) Measure the resistance between ENGINE-ECU connector 

B-21 terminal 86 and A/T-ECU connector B-19 terminal 5.

OK: 2 ohms or less

(5) Measure the resistance between ENGINE-ECU connector 

B-21 terminal 64 and A/T-ECU connector B-19 terminal 4.

OK: 2 ohms or less

NOTE: when diagnosing CAN-BUS on vehicles with 
manual transmission (M/T), disregard A/T-ECU and it’s wir-
ing circuits and check between ABS-ECU and 
ENGINE-ECU only.

CAUTION

Strictly observe the specified wiring harness repair proce-
dure. For details refer to 

P.54C-5

.

Q: Do all the resistances measure 2 ohms or less?

YES : If all the resistances measure 2 ohms or less, go to 

Step 3.

NO :  If either of the resistances measures more than 2 

ohms or all the resistances measure more than 2 
ohms, repair the wiring harness between 
ENGINE-ECU connector B-21 and the A/T-ECU 
connector B-19. 

16DB510A

HARNESS SIDE: B-19

TEST
HARNESS

TEST
HARNESS

HARNESS SIDE:  B-21

16DB511A

HARNESS SIDE: B-19

TEST
HARNESS

TEST
HARNESS

HARNESS SIDE:  B-21