Mitsubishi Galant 9G. Manual — part 1225

SERVICE PRECAUTIONS

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-4

SERVICE PRECAUTIONS

M1548302100043

WARNINGS IN DIAGNOSIS SECTION

DETAILS REGARDING WARNINGS

When servicing a CAN bus line, ground yourself
by touching a metal object such as an unpainted
water pipe. If you fail to do so, a component
connected to the CAN bus line may be damaged.

−

CAUTION

A digital multimeter should be used.

When measuring resistance value or voltage in
CAN bus lines, use a digital multimeter. If not
using a digital multimeter, the equipment
connected through the CAN communication
lines, may be damaged.

CAUTION

Disconnect the negative battery terminal.

Disconnect the negative battery terminal when
measuring the resistance value in the CAN bus
line. If you fail to do so, a component connected
through the CAN communication lines may be
damaged.

CAUTION

The test wiring harness should be used.

Always use the test harness when measuring the
voltage or resistance value at the female
connector. If you fail to do so, connectors may be
damaged.

CAUTION

The strand end of the twisted wire should be
within 10 cm (4 inches) from the connector.

If you repair the wire due to a defective
connector or its terminal or harness wire, you
should cut the wire so that the strand end of the
twisted wire should be within 10 cm (4 inches)
from the connector as shown. If it exceeds 10 cm
(4 inches), twist the wiring harness just like the
original twisted wire. If the strand end exceeds
10 cm (4 inches), a communication error may be
caused.

CAUTION

Strictly observe the specified wiring harness
repair procedure.

When you repair a CAN bus line, observe the
precautions on how to repair the CAN bus line
strictly (Refer to

P.54C-5

). If a new wire is added

or a splice point is modified for the CAN_L or
CAN_H line, an error in the CAN communication
may be caused.

AC203824

CONNECTOR

TWISTED WIRE

AB

10 cm
(4.0 inches)

PRECAUTIONS ON HOW TO REPAIR THE CAN BUS LINES

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-5

PRECAUTIONS ON HOW TO REPAIR THE CAN BUS LINES

M1548301900057

.

Precautions on how to repair the CAN bus lines

• If the CAN_L or CAN_H line on the main bus line or sub-bus

line is repaired, replace all the twisted wires between the
end connectors. If the wiring harness is partially repaired, or
only CAN_L or CAN_H line is repaired, noise suppression is
deteriorated, causing a communication error.

• If the connector or wire on the main bus line or the sub-bus

wire is replaced, the strand end of the twisted wire should
be within 10 cm (4 inches) from the connector. If it exceeds
10 cm (4 inches), twist the wiring harness just like the origi-
nal twisted wire. If the strand end exceeds 10 cm (4 inches),
noise suppression is deteriorated, causing a communica-
tion error.

• If a sub-bus line is repaired, splice a new wire directly into

the main bus line. If a new wire is spliced into the sub-bus
line, which is connected to another device, the CAN com-
munication will be disabled.

.

AC204696

ADDED WIRE

NO GOOD

AB

AC203824

CONNECTOR

TWISTED WIRE

AB

10 cm
(4.0 inches)

AC202856

ECU

ECU

ECU

ECU

GOOD

NO GOOD

OPEN
CIRCUIT
POINT

OPEN
CIRCUIT
POINT

AD

: MAIN BUS LINE

: SUB-BUS LINE

TERMINATOR RESISTOR

TERMINATOR RESISTOR

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

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-6

Precautions on how to repair the
terminator resistor

If one-side of the terminator resistors is broken, the
CAN communication will continue, although noise
suppression is deteriorated. In this case, no DTC
may be set. Check the system regardless of whether
a DTC is set or not. If damage is found, replace the
terminator resistor.

EXPLANATION ABOUT THE SCAN TOOL (MUT-III) CAN

BUS DIAGNOSTICS

M1548300100058

The MUT-III CAN bus diagnostics carries out the
three checks below automatically, and then displays
the current condition of the CAN bus lines according
to the check results.

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

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

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

TSB Revision

CONTROLLER AREA NETWORK (CAN)

54C-7

(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.

(3) Checking the communication condition of

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

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

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 −