Mitsubishi Grandis. Manual — part 478

EXPLANATION ABOUT THE MUT-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54D-10

CAN Bus Line Diagnostic Flow

1. MUT-III CAN bus diagnostics

The MUT-III diagnoses CAN bus lines in
accordance with the following strategy.

NOTE: When the MUT-III carries out the
voltage and resistance measurements, it will
cease the communication between each of the
ECU. If the MUT-III can not cease the
communication, it will carry out the voltage
measurement.

(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 earth.

(2) Measuring resistance in CAN bus line

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

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)

NG

AE

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

Terminal to be
diagnosed

Normal value

Measure
ment
value

Trouble when the
measurement value
does not meet the
normal value

Note

Measuring the voltage
between the CAN_L line
and body earth

1.0 V or more and 4.0
V or less

Less than
1.0 V

Short to earth of the
CAN_L line

If the CAN_L or H line
is shorted to earth or
power supply, a
diagnosis code may
not be set.

More than
4.0 V

Short to power
supply of the CAN_L
line

Measuring the voltage
between the CAN_H line
and body earth

1.0 V or more and 4.0
V or less

Less than
1.0 V

Short to earth of the
CAN_H line

More than
4.0 V

Short to power
supply of the CAN_H
line

EXPLANATION ABOUT THE MUT-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54D-11

Checks the terminator resistors (incorporated
in the combination meter or the
engine-A/T-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 are as follows.

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 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
diagnosis connector and
main bus line

-

2

Ω 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 MUT-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54D-12

AC204741

DATA LINK
CONNECTOR

ECU B

ECU C

ECU D

ECU A

(a)

(b)

(c)

(d)

(e)

(f)

(g)

AC

REFERENCE CIRCUIT

EXPLANATION ABOUT THE MUT-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54D-13

ECU which
cannot
communicate
with the
MUT-III

Possible
trouble spot

Logic for narrowing 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)