Mitsubishi Lancer (4A9 engine). Manual - part 247

EXPLANATION ABOUT THE M.U.T.-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54C-12

ECU which 
cannot 
communicate 
with the 
M.U.T.-III

Possible 
trouble spot

Logic for narrowing down trouble spot

ETACS-ECU 
and all ECUs

CAN bus line 
(h) and power 
supply system 
to ETACS-
ECU

The ETACS-ECU and the other 
ECUs use the CAN bus line (h) 
when they communicate with the 
M.U.T.-III. Since none of the 
ETACS-ECU and the other ECUs 
can communicate with the 
M.U.T.-III, CAN bus line (h) or the 
power supply circuit to the 
ETACS-ECU may be faulty.

AC204742BO

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

ECU A

CAN bus line 
(a) and power 
supply system 
to ECU A

ECU A communicates with the 
M.U.T.-III via CAN bus lines (a) 
and (b). The M.U.T.-III judges that 
CAN bus line (b) is normal, 
because it can communicate with 
other ECUs. Possible trouble may 
be present in CAN bus line (a) or 
the power supply system to ECU 
A.

AC204742BH

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

ECU C

CAN bus line 
(g) and power 
supply system 
to ECU C

ECU C communicates with the 
M.U.T.-III via CAN bus lines (b), 
(c), (d) and (g). The M.U.T.-III 
judges that CAN bus lines (b), (c) 
and (d) are normal, because it 
can communicate with ECUs B 
and D. Possible trouble may be 
present in CAN bus line (g) or the 
power supply system to ECU C.

AC204742BI

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

EXPLANATION ABOUT THE M.U.T.-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54C-13

2. Pinpoint possible trouble spot according to 

diagnosis code
If diagnosis code related to CAN communication 
is set as past trouble, isolate opens as described 
below.

NOTE: If you pinpoint trouble spot according to 
diagnosis code, you should use time-out diagno-
sis code. diagnosis code related to failure infor-
mation is set when the data to be set contains an 
error, so CAN bus line itself is probably normal.

ECU C and 
ECU D

Trouble in 
CAN bus line 
(d)

ECUs C and D communicate with 
the M.U.T.-III via CAN bus lines 
(b), (c), (d), (e) and (g). The 
M.U.T.-III judges that CAN bus 
lines (b) and (c) are normal, 
because it can communicate with 
ECU B. Possible trouble may be 
present in CAN bus line (d), (e) or 
(g) or the power supply system to 
ECU D or C. CAN bus line (d) is 
shared by ECUs C and D when 
they communicate with the 
M.U.T.-III, so CAN bus line (d) is 
suspected as ultimate cause. 
CAN bus line (g) or (e) and power 
supply systems to ECU C or D 
are also suspected as second 
cause.

AC204742BJ

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

ECU B and 
ECU D

CAN bus line 
(e) or (f) or 
power supply 
system to ECU 
B or D

ECUs B and D communicate with 
the M.U.T.-III via CAN bus lines 
(b), (c), (d), (e) and (f). The 
M.U.T.-III judges that CAN bus 
lines (b), (c) and (d) are normal, 
because it can communicate with 
ECU C. Possible trouble may be 
present in CAN bus line (f) or (e) 
or the power supply system to 
ECU B or D.

AC204742BK

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

All ECU (except 
ETACS-ECU)

CAN bus line 
(b)

The other ECUs except the 
ETACS-ECU use CAN bus lines 
(b) and (h) when they 
communicate with the M.U.T.-III. 
It must be assumed that CAN bus 
line (b) is defective since the 
ETACS-ECU can communicate 
with the M.U.T.-III.

AC204742BP

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

ECU which 
cannot 
communicate 
with the 
M.U.T.-III

Possible 
trouble spot

Logic for narrowing down trouble spot

EXPLANATION ABOUT THE M.U.T.-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54C-14

NOTE: Time-out diagnosis code codes are stored 
in each ECU memory individually. Therefore, it is 
possible that these diagnosis code codes have 
not been set simultaneously. If the trouble spot 
cannot be found when you diagnose by judging 
from multiple diagnosis code codes, check the 
communication lines between each ECU.

Diagnosis 
code to be set

Possible 
trouble spot

Logic for narrowing down trouble spot

Time-out 
diagnosis code 
associated with 
ECU D is stored 
in ECU A, ECU 
B and ECU C.

Trouble in 
CAN bus line 
(e) and power 
supply system 
to ECU D

When time-out diagnosis code 
associated with ECU D is stored 
in ECU A, B and C, or time-out 
diagnosis codes associated with 
ECUs A, B and C are stored in 
ECU D, or "bus off" diagnosis 
code is stored in ECU D, CAN 
bus line (e) is suspected. When 
diagnosis code is not stored in 
ECU D, the power supply to ECU 
D is suspected.

AC204742BL

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

Time-out 
diagnosis codes 
associated with 
ECUs A, B and 
C are stored in 
ECU D.
"Bus off" 
diagnosis code 
is stored in ECU 
D.
Time-out 
diagnosis code 
associated with 
ECU A is stored 
in ECUs B, C 
and D.

Trouble in 
CAN bus line 
(a) or (c) and 
power supply 
system to ECU 
A.

When time-out diagnosis code 
associated with ECU A is stored 
in ECUs B, C and D, or time-out 
diagnosis codes associated with 
ECUs B, C and D are stored in 
ECU A, or "bus off" diagnosis 
code is stored in ECU A, CAN 
bus line (a) or (c) is suspected. 
When diagnosis code is not 
stored in ECU A, the power 
supply to ECU A is suspected.

AC204742BM

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

Time-out 
diagnosis codes 
associated with 
ECUs B, C and 
D are stored in 
ECU A.
"Bus off" 
diagnosis code 
is stored in ECU 
A.

TROUBLESHOOTING

CONTROLLER AREA NETWORK (CAN)

54C-15

TROUBLESHOOTING

CAN BUS DIAGNOSTICS TABLE

M1548300202589

CAUTION

• A diagnosis code may not also be set in the 

CAN-B lines under the conditions below. If no 
diagnosis code has been set due to electrical 
noise, confirm diagnosis item 25 .

• Open circuit at the CAN_H side of the 

CAN-B bus lines

• Open circuit at the CAN_L side of the CAN-

B bus line

• Short to earth at the CAN_H side of the 

CAN-B bus line

• During diagnosis, a diagnosis code associ-

ated with another system may be set when 
the ignition switch is turned on with connec-
tor(s) disconnected. After completing the 

repair, confirm all systems for diagnosis 
code(s). If diagnosis code(s) are set, erase 
them all.

This diagnosis applies only to the CAN bus lines. If a 
different system is defective, proceed to the applica-
ble diagnosis section for each system. Observe the 
diagnosis procedure below only when the CAN bus 
line is defective.

Time-out 
diagnosis codes 
associated with 
ECUs C and D 
are stored in 
ECU A and 
ECU B.

Trouble in 
CAN bus line 
(d)

If time-out diagnosis codes 
associated with ECUs C and D 
are stored in ECUs A and B, or 
time-out codes associated with 
ECUs A and B are stored in 
ECUs C and D, CAN bus line (d) 
is suspected. CAN bus line (g) or 
(e) and power supply systems to 
ECU C or D are also suspected 
as second cause.

AC204742 BR

DATA LINK 

CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Time-out 
diagnosis codes 
associated with 
ECUs A and B 
are stored in 
ECU C and 
ECU D.
Time-out 
diagnosis codes 
associated with 
ECUs A, B, C 
and D are 
stored in 
ETACS-ECU.

Trouble in 
CAN bus line 
(b)

It must be assumed that a fault 
was present in CAN bus line (b) 
when the ETACS-ECU has set a 
time-out diagnosis code for ECU 
A, B, C and D.

AC204742BP

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

ETACS-ECU
(Gateway)

Diagnosis 
connector

Time-out 
diagnosis code 
associated with 
ETACS-ECU is 
stored in ECU 
A, B, C and 
ECU D.

Diagnosis 
code to be set

Possible 
trouble spot

Logic for narrowing down trouble spot