Mitsubishi Lancer (4A9 engine). Manual — part 250

TROUBLESHOOTING

CONTROLLER AREA NETWORK (CAN)

54C-24

CAN BUS DIAGNOSIS

Diagnosis Item 1: Diagnose when the M.U.T.-III cannot receive the data sent by ETACS-ECU

CAUTION

When servicing a CAN bus line, earth yourself by touching a metal object such as an unpainted water
pipe. If you fail to do, a component connected to the CAN bus line may be broken.

Diagnosis CAN Communication Circuit

ETACS-ECU

DIAGNOSIS
CONNECTOR

CAN DRIVE
CIRCUIT

INTERFACE
CIRCUIT

FRONT SIDE

Wire colour code
B : Black LG : Light green G : Green L : Blue W : White Y : Yellow SB : Sky blue
BR : Brown O : Orange GR : Grey R : Red P : Pink V : Violet PU : Purple SI : Silver

AC709893

C-26 (B)

Connector: C-26 <LHD>

AK

AC709897

C-26 (B)

Connector: C-26 <RHD>

AD

ACA00886

BE

Connector: C-301 <LHD>
ETACS-ECU

ACA00887

BF

Connector: C-301 <RHD>
ETACS-ECU

TROUBLESHOOTING

CONTROLLER AREA NETWORK (CAN)

54C-25

FUNCTION
When the CAN bus diagnosis is carried out, the
M.U.T.-III communicates with the ETACS-ECU. If a
communication flag is not set for the ETACS-ECU,
the ETACS-ECU will be diagnosed as a communica-
tion error.

TROUBLE JUDGEMENT CONDITIONS
If a communication flag is not set for the ETACS-
ECU, the M.U.T.-III determines that there is a failure.

TROUBLESHOOTING HINTS

• Malfunction of the connector (diagnosis connec-

tor or ETACS-ECU connector improperly con-
nected)

• Malfunction of the wiring harness (open circuit,

short to earth, short to power supply system
between the diagnosis connector and the
ETACS-ECU connector, line-to-line short, or
power supply line to the ETACS-ECU)

• Malfunction of ETACS-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: C-26 diagnosis
connector and C-301 ETACS-ECU connector

CAUTION

The strand end of the twist wire should be within
10 cm from the connector. For details refer to .

Q: Is the check result normal?

YES :

Go to Step 2.

NO :

Repair the defective connector.

STEP 2. Check the wiring harness between C-26
diagnosis connector and C-301 ETACS-ECU
connector for the continuity

CAUTION

Strictly observe the specified wiring harness
repair procedure. For details refer to .
(1) Disconnect the M.U.T.-III and ETACS-ECU

connector, and measure at the wiring harness
side.

(2) Measure the continuity between C-26 diagnosis

connector terminal No.6 and C-301 ETACS-ECU
connector terminal No.5 <CAN_H>

OK: Continuity exists (2

Ω or less)

(3) Measure the continuity between C-26 diagnosis

connector terminal No.14 and C-301 ETACS-
ECU connector terminal No.4 <CAN_L>

OK: Continuity exists (2

Ω or less)

Q: Is the check result normal?

YES :

Go to Step 3.

NO :

Repair the wiring harness.

STEP 3. Check the wiring harness between C-26
diagnosis connector and C-301 ETACS-ECU
connector for short to earth (resistance
measurement).

CAUTION

• Disconnect the negative battery terminal. For

details refer to .

• A digital multimeter should be used. For

details refer to .

• The test wiring harness should be used. For

details refer to .

• Strictly observe the specified wiring harness

repair procedure. For details refer to .

(1) Disconnect the M.U.T.-III and the ETACS-ECU

connector, and measure at the wiring harness
side.

(2) Measure the resistance between C-26 diagnosis

connector terminal No.6 and body earth.
<CAN_H>

OK: 1 k

Ω or more

(3) Measure the resistance between C-26 diagnosis

connector terminal No.14 and body earth.
<CAN_L>

OK: 1 k

Ω or more

Q: Is the check result normal?

YES :

Go to Step 4.

NO :

Repair the wiring harness.

STEP 4. Check the wiring harness between C-26
diagnosis connector and C-301 ETACS-ECU
connector for short to power supply (voltage
measurement).

CAUTION

• A digital multimeter should be used. For

details refer to .

• The test wiring harness should be used. For

details refer to .

• Strictly observe the specified wiring harness

repair procedure. For details refer to .

(1) Disconnect the M.U.T.-III and the ETACS-ECU

connector, and measure at the wiring harness
side.

(2) Turn the ignition switch to the ON position.
(3) Measure the voltage between C-26 diagnosis

connector terminal No.6 and body earth.
<CAN_H>

OK: 1 V or less

(4) Measure the voltage between C-26 diagnosis

TROUBLESHOOTING

CONTROLLER AREA NETWORK (CAN)

54C-26

connector terminal No.14 and body earth.
<CAN_L>

OK: 1 V or less

Q: Is the check result normal?

YES :

Go to Step 5.

NO :

Repair the wiring harness.

STEP 5. Check the wiring harness between C-26
diagnosis connector and C-301 ETACS-ECU
connector for line-to-line short (resistance
measurement).

CAUTION

• Disconnect the negative battery terminal. For

details refer to .

• A digital multimeter should be used. For

details refer to .

• The test wiring harness should be used. For

details refer to .

• Strictly observe the specified wiring harness

repair procedure. For details refer to .

(1) Disconnect the M.U.T.-III and the ETACS-ECU

connector, and check that there is continuity at
the harness side.

(2) Check that there is continuity between C-26

diagnosis connector terminal Nos.6 and 14.

OK: No Continuity

Q: Is the check result normal?

YES :

Go to Step 6.

NO :

Repair the wiring harness.

STEP 6. Trouble symptom check
Diagnose the CAN bus line, and check that normal
condition is displayed.

Q: Is the check result normal?

YES :

The trouble can be an intermittent

malfunction (Refer to GROUP 00

− How to

use Troubleshooting/inspection Service
Points

− How to Cope with Intermittent

Malfunction ).

NO :

Replace the ETACS-ECU.

Diagnosis Item 2: Malfunction of the ETACS-ECU

CAUTION

When servicing a CAN bus line, earth yourself by
touching a metal object such as an unpainted
water pipe. If you fail to do, a component con-
nected to the CAN bus line may be broken.
FUNCTION
When the CAN bus diagnosis is carried out, the
M.U.T.-III sets communication "OK" flags in the patch
between the ETACS-ECU and active other ECUs. If
a commutation "OK" flag is not set for the ECUs
other than the ETACS-ECU, this diagnosis result will
be set.

TROUBLE JUDGMENT CONDITIONS
If no communication flags are set for the ECUs (on
the CAN-B or CAN-C lines) other than the ETACS-
ECU, the ETACS-ECU determines that there is a fail-
ure.

TROUBLESHOOTING HINTS

• Malfunction of the ETACS-ECU

DIAGNOSIS PROCEDURE

M.U.T.-III other system diagnosis code
Check whether ETACS-ECU-related diagnosis code
is set.

Q: Is the diagnosis code set?

The diagnosis code other than the U code is set. :

Troubleshoot the ETACS-ECU. Refer to
GROUP 54A

− ETACS-ECU .

Only U-code diagnosis code is set or the diagnosis
code is not set. :

Check the power supply circuit of

the ETACS-ECU. Refer to GROUP 54A

−

ETACS-ECU .

TROUBLESHOOTING

CONTROLLER AREA NETWORK (CAN)

54C-27

Diagnosis Item 3: Abnormal short between the CAN-C bus lines

CAUTION

When servicing a CAN bus line, earth yourself by touching a metal object such as an unpainted water
pipe. If you fail to do, a component connected to the CAN bus line may be broken.