Mitsubishi Galant (2004+). Manual - part 349

 

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Mitsubishi Galant (2004+). Manual - part 349

 

 

EXPLANATION ABOUT THE SCAN TOOL (MUT-III) CAN BUS DIAGNOSTICS

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-7

1. MUT-III CAN bus diagnostics

The MUT-III diagnoses CAN bus lines in 
accordance with the following strategy.
(1) Measuring voltage in CAN bus line 

Diagnoses the power supply (such as wires of 
higher voltage than CAN communication line) 
and grounding (such as wires of lower voltage 
than CAN communication line) of CAN bus 
lines for short circuit by measuring the 
voltages between the CAN_L line or H line and 
body ground.

(2) Measuring resistance in CAN bus line 

Checks the terminator resistors (incorporated 
in the combination meter or the powertrain 
control module), which are connected to each 
end of a CAN bus line, for breakage and a 
CAN bus main line for open circuit by 
measuring the resistance value between a 
CAN_L line and H line.

MEASURE THE 
VOLTAGE

NORMAL VALUE

MEASUREMENT 
VALUE

TROUBLE WHEN THE 
MEASUREMENT VALUE DOES NOT 
MEET THE NORMAL VALUE

NOTE

Between the 
CAN_L line and 
body ground

1.0 V or more and 
4.0 V or less

Less than 
1.0 V

Short to ground of the 
CAN_L line

If the CAN_L or H line 
is shorted to ground or 
power supply, a DTC 
may not be set.

More than 
4.0 V

A short to the power supply 
of the CAN_L line

Between the 
CAN_H line and 
body ground

1.0 V or more and 
4.0 V or less

Less than 
1.0 V

Short to ground of the 
CAN_H line

More than 
4.0 V

A short to the power supply 
of the CAN_H line

NORMAL 
VALUE

MEASUREMENT VALUE

TROUBLE WHEN THE 
MEASUREMENT VALUE DOES 
NOT MEET THE NORMAL VALUE

NOTE

60 

± 10 Ω

120 

± 20 Ω

Trouble in a CAN main bus 
line or terminator resistor

If only one terminator resistor is broken at 
either side, the CAN communication will 
continue although noise suppression is 
deteriorated.
If a CAN main bus line is open circuit, the 
CAN communication is suspended at that 
open circuit point.

No continuity

Trouble in CAN main bus 
line or between the data 
link connector and main 
bus line

−

2 ohms or less

CAN bus line (between 
CAN_L and H lines) is 
shorted

If a CAN bus line is shorted, all ECUs cease 
communicating each other (This fail-safe 
function is called "Bus off").

Other than above

Poorly engaged connector −

EXPLANATION ABOUT THE SCAN TOOL (MUT-III) CAN BUS DIAGNOSTICS

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-8

(3) Checking the communication condition of 

ECUs

The MUT-III narrows down troubles in circuit 
by itself. Its strategy is as follows:

AC204741

DATA LINK 
CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

AC

REFERENCE CIRCUIT

ECU WHICH 
CAN NOT 
COMMUNICATE 
WITH THE 
MUT-III

POSSIBLE 
TROUBLE 
SPOT

LOGIC FOR DETERMINING DOWN TROUBLE SPOT

ECU A

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

ECU A communicates with the 
MUT-III via CAN bus lines (a) and 
(b). The MUT-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.

AC204742 AZ

DATA LINK 
CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

EXPLANATION ABOUT THE SCAN TOOL (MUT-III) CAN BUS DIAGNOSTICS

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-9

ECU C

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

ECU C communicates with the 
MUT-III via CAN bus lines (b), (c), 
(d) and (g). The MUT-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.

ECU C and 
ECU D

Trouble in 
CAN bus line 
(d)

ECUs C and D communicate with 
the MUT-III via CAN bus lines (b), 
(c), (d), (e) and (g). The MUT-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. CAN bus line (d) is shared by 
ECUs C and D when they 
communicate with the MUT-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.

ECU B and 
ECU D

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

ECUs C and D communicate with 
the MUT-III via CAN bus lines (b), 
(c), (d), (e) and (g). The MUT-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.

ECU WHICH 
CAN NOT 
COMMUNICATE 
WITH THE 
MUT-III

POSSIBLE 
TROUBLE 
SPOT

LOGIC FOR DETERMINING DOWN TROUBLE SPOT

AC204742 BA

DATA LINK 

CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

AC204742 BB

DATA LINK 

CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

AC204742 BC

DATA LINK 

CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

EXPLANATION ABOUT THE SCAN TOOL (MUT-III) CAN BUS DIAGNOSTICS

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-10

2. If DTC code related to CAN communication is set 

as past trouble, isolate opens as described below.
NOTE: If you pinpoint trouble spot according to 
DTC code, you should use time-out DTC code. 
DTC code related to failure information is set 
when the data to be set contains an error, so CAN 
bus line itself is probably normal.

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

DTC CODE TO 
BE SET

POSSIBLE 
TROUBLE 
SPOT

LOGIC FOR DETERMINING TROUBLE SPOT

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

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

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

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

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

AC204742 BD

DATA LINK 

CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

AC204742 BE

DATA LINK 

CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

AC204742 BF

DATA LINK 

CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

 

 

 

 

 

 

 

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