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)