Mitsubishi 380. Manual - part 649

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

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.

AC204700

GO TO ORDINARY DIAGNOSIS

SHORT IN CAN BUS LINE TO
POWER SUPPLY OR GROUND

1. MUT-III CAN BUS
DIAGNOSTICS

(2) MEASURING RESISTANCE IN
CAN BUS LINE

OK FOR (2) AND (3)
P CODE, B CODE,
C CODE OR
U CODE (CURRENT
TROUBLE)

OK FOR (2) AND (3)
U CODE (PAST TROUBLE)

NG FOR (2) OR (3)

FROM OTHER DIAGNOSIS

· OPEN CIRCUIT IN CAN BUS LINE
· BROKEN TERMINATOR RESISTOR
· POWER SUPPLY TO ECU POORLY
GROUNDED

2. PINPOINT POSSIBLE TROUBLE
SPOT ACCORDING TO DTC CODE

(1) MEASURING VOLTAGE IN
CAN BUS LINE

(3) CHECK ECU WHICH MUT-III IS
COMMUNICATING WITH

MEASURE THE
VOLTAGE

NORMAL
VALUE

MEASURE
MENT
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

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

CONTROLLER AREA NETWORK (CAN)

54C-8

(2) Measuring resistance in CAN bus line

Checks the terminator resistors (incorporated
in the combination meter or the
ENGINE-ECU), 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.

(3) Checking the communication condition of

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

NORMAL
VALUE

MEASUREMENT
VALUE

TROUBLE WHEN THE
MEASUREMENT VALUE
DOES NOT MEET THE
NORMAL VALUE

NOTE

± 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 DIAGNOSTIC TOOL (MUT-III) CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54C-9

AC204741

DATA LINK
CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

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 DIAGNOSTIC TOOL (MUT-III) CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54C-10

2. If DTC code related to CAN communication is set

as past trouble, isolate opens as described below.

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)

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