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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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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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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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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