Mitsubishi Colt Ralliart. Manual — part 294

SERVICE PRECAUTIONS

CONTROLLER AREA NETWORK (CAN)

54D-5

SERVICE PRECAUTIONS

M1548302100117

Warnings in diagnosis section

Details regarding warnings

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

−

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 equipments, which
are connected through the CAN communication
lines, may be damaged.

When measuring the resistance, 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, the equipments, which
are connected through the CAN communication
lines, may be damaged.

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.

The strand end of the twist wire should be within
10 cm from the connector.

AC203824

10 cm

Connector

Twisted wire

AB

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
twist wire should be within 10 cm from the
connector as shown. If it exceeds 10 cm, twist
the wiring harness just like the original twisted
wire. If the strand end exceeds 10 cm (4.0
inches), a communication error may be caused.

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.54D-6

. 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.

CAUTION

CAUTION

CAUTION

CAUTION

CAUTION

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TOC

PRECAUTIONS ON HOW TO REPAIR THE CAN BUS LINES

CONTROLLER AREA NETWORK (CAN)

54D-6

PRECAUTIONS ON HOW TO REPAIR THE CAN BUS LINES

M1548301900121

PRECAUTIONS ON HOW TO REPAIR THE
CAN BUS LINES

AC204696

Added wire

No good

4AB

• If the CAN bus line(s) are repaired, renew 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 suppres-
sion is deteriorated, causing a communication
error.

AC203824

10 cm

Connector

Twisted wire

AB

•

AC202856

ECU

ECU

ECU

ECU

Good

No good

Terminator resistor

Open
circuit
point

Open
circuit
point

Terminator resistor

AB

If the connector or wire on the main bus line or
the sub-bus wire is replaced, the frayed end of
the twisted wire should be within 10 cm from the
connector. If it exceeds 10 cm, twist the wiring
harness just like the original twisted wire. If the
frayed end exceeds 10 cm, noise suppression is
deteriorated, causing a communication 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 communication will
be disabled.

PRECAUTIONS ON HOW TO REPAIR THE
TERMINATOR RESISTOR

If one-side terminator resistor is broken, the CAN
communication will continue although noise suppres-
sion is deteriorated. No diagnosis codes may be set
even if the terminator resistor was broken. If a dam-
age is found, replace the ECU which incorporates
the defective terminator resistor.

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Index

Group

TOC

EXPLANATION ABOUT THE M.U.T.-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54D-7

EXPLANATION ABOUT THE M.U.T.-III CAN BUS

DIAGNOSTICS

M1548300100393

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

CAN BUS LINE DIAGNOSTIC FLOW

AC204700

Go to ordinary diagnosis

Short in CAN bus line to power
supply or ground

1. M.U.T.-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 diagnosis code

(1) Measuring voltage in CAN bus line

(3) Check ECU which M.U.T.-III is
communicating with

1. M.U.T.-III CAN bus diagnostics

The M.U.T.-III diagnoses CAN bus lines in
accordance with the following strategy.

NOTE: When the M.U.T.-III carries out the volt-
age and resistance measurements, it will
cease the communication between each of the
ECU. If the M.U.T.-III can not cease the com-
munication, it will carry out the voltage meas-
urement.

(1) Measuring voltage in CAN bus line

Diagnoses the power supply (such as wires of
higher voltage than CAN communication line)
and earthing (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.

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Index

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TOC

Terminal to be
diagnosed

Normal value

Measurement
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. 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. 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. Short to earth of the

CAN_H line

More than 4.0. Short to power

supply of the CAN_H
line

EXPLANATION ABOUT THE M.U.T.-III CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54D-8

(2) Measuring resistance in CAN bus line

Checks the terminator resistors (incorporated
in the combination meter or the engine-ECU
<M/T> or engine-CVT-ECU <CVT>), 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.

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 −

(3) Checking the communication condition of

ECUs

The M.U.T.-III narrows down troubles in circuit
by itself. Its strategy is as follows.

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