Mitsubishi Outlander (2013+). Manual — part 115

SYSTEM OPERATION

CONTROLLER AREA NETWORK (CAN)

54C-5

• When data frames conflict with one another

(when plural ECUs transmit signals simultane-
ously), data is prioritised for transmission by
mediation, therefore, plural data frames are not
sent simultaneously. For further details, consult
the mediation section.

• Data is transmitted not by the conventional volt-

age-using method but by voltage potential differ-
ence. For further details, consult the section on
CAN bus voltage transformation .

• Reliability of each ECU transmitting signals via

CAN communication is secured by several error
detection and recovery processes. For further
details, consult the sections on error detection
and system recovery.

• For major communication signals (transmitting

signals) among ECUs.

MEDIATION

Because each ECU transmits data independently on
the CAN bus, there are cases of data collision when
multiple data frames that ECUs attempt to transmit
simultaneously (if multiple ECUs transmit at nearly
the same moment). At this moment, processing of
the ECUs attempting transmission is performed in
the following way.

1. Data frame with high priority is transmitted first

according to ID codes memorized in data frames.

2. Transmission of low-priority data (data frames) is

suspended by the issuing ECUs until the bus
clears (when no transmission data exists on the
CAN bus).

NOTE: If the suspended state continues for a spe-

cific time, new data (data frame content) is cre-
ated and sent.

3. ECU containing suspended data frames trans-

mits the data when the bus becomes available.

NOTE: There is enough capacity on the CAN bus,
which never prevents data frames from being sent.

VOLTAGE TRANSFORMATION ON THE CAN BUS

Data frame transmission through the CAN bus line
involves voltage transformation (for output signals) in
the distinctive CAN profile as follows. The ECU
transmitting through the CAN_H and CAN_L bus
lines sends 2.5

− 3.5 V signals to the CAN_H side

and 2.5

− 1.5 V signals to the CAN_L side. The

receiving ECU reads the data from the CAN_H and
CAN_L potential difference. "Recessive" refers to the
state where both CAN_H and CAN_L are under the
2.5 V state, and "Dominant" refers to the state where

CAN_H is under the 3.5 V state and CAN_L is under
the 1.5 V state. By transformation mainly to 2.5 V,
even in cases when voltage is rendered 0 from faulty
earthing or the like (causing a problem of an approxi-
mate 0.5 voltage increase on the communications
line), communication can be continued uninter-
rupted. Employing dual communications lines
improves reliability to prevent the presence of noise,
compared to the conventional communication
method.

AC204753

Voltage
transformation
in CAN_L

State:

Logical value:

Recessive

Dominant

3.5 V

2.5 V

1.5 V

Voltage
transformation
in CAN_H

SELF-DIAGNOSIS

CONTROLLER AREA NETWORK (CAN)

54C-6

DATA FRAMES

The data frame, which is sent from each ECU (or
sensor) to the CAN bus line, consists of the fields
bellow.

SOF (Start of Frame)

• Indicates the start of the frame

ID (Identifier) region

• Identifies the data content while specifying prior-

ity rank in case of mediation

Control region

• Specifies the frame type, data length, etc.

Data region

• Values used for data control, etc.

CRC (Cyclic Redundancy Check) region

• Region where to check for errors in sent data.

The transmitting ECU calculates data regions by
applying prescribed operations and stores the
results. The receiving ECU detects erroneous
communication by comparing the CRC region
with the data region.

ACK (Acknowledge) region

• Region where to conform the reception of sent

data

EOF (End of Frame)

• Indicates the end of the frame

ERROR DETECTION AND RECOVERY

CAN protocol secures its reliability of communication
by providing several error detection function such as
CRC shown in data frame, and the recovery function
(recovery is performed by resending, from abnormal
state such as transmission errors). If an error is
detected but it is not resolved even after recovery,
communication is stopped. This state is called "Bus
Off."

SELF-DIAGNOSIS

M2542000400428

• CAN self-diagnosis is performed by each ECU

connected to the CAN bus.

• Diagnosis codes related to communication are

named with the capital letter U, and are called
"U-codes."

• A summary of the CAN self-diagnosis system is

presented below.

TIME-OUT

Each ECU transmits data frames periodically. If the
data frame is not received within the specified period,
the intended receiving ECU transmits a diagnosis
code indicating communication time-out for the ECU
that failed to transmit.

FAILURE DATA

When the transmitting ECU detects failure of a sen-
sor directly connected to it, this is the pertinent data
used to inform the ECU.

AC404606

SOF

EOF

ID region

CRC region

ACK

region

Control

region

Data region

Data Frames

CAN BUS DIAGNOSTICS

CONTROLLER AREA NETWORK (CAN)

54C-7

CAN BUS DIAGNOSTICS

M2542000500339

As ECUs are connected via CAN bus (including
M.U.T.-III), always diagnose CAN bus to confirm its
normality when inspecting. When the CAN bus diag-
nosis is carried out, the M.U.T.-III will monitor the
mutual communication status of the ECUs and then
display a current status of the CAN bus on its screen.

55-1

GROUP 55

HEATER, AIR

CONDITIONER AND

VENTILATION

CONTENTS

GENERAL INFORMATION . . . . . . . .

55-2

HEATER AND AIR CONDITIONER SYSTEM

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

55-7

HEATER CONTROL . . . . . . . . . . . . .