CAN SYSTEM DESCRIPTION

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Mechanism of CAN System-Related Module

•  A CAN system-related module is composed of an electrical circuit, CPU, and input/output interface.
•  The size of the module has been reduced due to the elimination of the bulky, superfluous, input/output interface in the conventional type of electrical module.
•  The CPU (multiplex block) controls all signals exchanged on the CAN harness.
•  Communication with non-multiplex parts is carried out by conventional input/output interface.
•  The functions of each component are shown below.

Component

Function
Electrical circuit
Supplies power to CPU and vicinity, and to input/output interface.
CPU
Computation processing block
Control function has been expanded, and when transmission is necessary, transmitted data is stored in a multiplex block. If a multiplex block receives a request to read stored data, transmitted data is read from the multiplex block.
Multiplex block
Transmits data received from bus line to computation processing block. In addition, sends transmitted data stored from computation processing block to bus line.
Input/Output interface
Electrically converts information signals from switches to, be input to CPU, and signals output from CPU for operating actuator or indicator lights.

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Twisted Pair

•  The multichannel use two spirally twisted wires called a twisted pair, and each wire, CAN_L and CAN_H, has its own special function.
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•  Both bus lines are opposite phase voltage. This allows for minimal noise being emitted and makes if difficult for noise interference to be received.

Time Division Multiplex

•  For information exchange between electrical modules in a conventional system, a wire connection was necessary for each information signal. However, by sending the different signal at varying times over one channel, it is possible to send a large amount of information via a small harness.
•  In the conventional, non-multiplex system, in order to control the illumination of the five bulbs, one switch and one channel was necessary for each bulb. For bulbs B and C to illuminate, switches B and C must be ON and electricity must flow through the channel. With the time multiplex system, this can be done through one channel. The channel is comprised of five data signal transmitters which transmit either a “0” or “1” signal to indicate whether a bulb turns ON or OFF. For example, to illuminate bulbs B and C, transmitters B and C transmit a “1” and transmitters A, D, and E transmit a “0”. When the receiver receives these signal, bulbs B and C illuminate.
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Vehicle CAN System

•  By rearranging the multiple signal, common information between the CAN system-related modules is transmitted and received through the multichannel.
•  The signal transmitted by one CAN system-related module is sent through the multichannel to all the CAN system-related modules, but only the concerned module (s) receives the signal and performs the appropriate operation (ex. light illumination, fan operation).
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CAN Signal-Chart (HS-CAN)

OUT: Output (sends signal)
IN: Input (receives signal)

Signal

Multiplex module

PCM

TCM

DSC/RSC HU/CM

BCM

4WD control module

PLG control module

SAS control module

Keyless control module

Instrument cluster

Engine-off-natural-vacuum
Immobilizer-related information
OUT
–
–
–
–
–
–
IN
IN
–
IN
–
–
–
–
–
–
OUT
–
–
Engine torque
OUT
IN
–
–
–
–
–
–
–
–
Engine load
OUT
IN
–
–
–
–
–
–
–
–
Engine torque
OUT
–
IN
–
–
–
–
–
–
–
OUT
IN
–
–
–
–
–
–
–
–
Brake switch
OUT
–
IN
–
–
–
–
–
–
–
Malfunction of evaporative emission control system-related information
OUT
–
–
–
–
–
–
–
–
IN
IN
–
–
–
–
–
–
–
–
OUT
FUEL_FLOW
OUT
–
–
–
–
–
–
–
IN
–
MIL on request
OUT
–
–
–
–
–
–
–
IN
–
IN
OUT
–
–
–
–
–
–
–
–
Cruise control system-related information
OUT
–
–
–
–
–
–
–
IN
–
OUT
–
IN
–
–
–
–
–
IN
–
ETC warning light on request
OUT
–
–
–
–
–
–
–
IN
–
Electronic throttle control (ETC) status
OUT
–
–
–
–
–
–
–
IN
–
Generator warning light on request
OUT
–
–
–
–
–
–
–
IN
–
Fuel cap warning light on request
OUT
–
–
–
–
–
–
–
IN
–
Intake air temperature
OUT
–
IN
–
–
–
–
–
–
–
Engine coolant temperature
OUT
IN
–
–
–
–
–
–
–
–
ATX gear position/selector lever position
OUT
–
IN
–
–
–
–
–
–
–
Steering angle/steering angle sensor status
–
–
IN
OUT
–
–
–
–
–
–
Door switch status (LF, RF, LR, RR, liftgate)
–
–
IN
OUT
–
–
–
–
IN
–
Key reminder switch status
–
–
–
OUT
–
–
–
–
IN
–
Turn indicator light on request
–
–
–
OUT
–
–
–
–
IN
–
Turn indicator light on request
–
–
–
OUT
–
–
–
–
IN
–
Brake fluid level
–
–
–
OUT
–
–
–
–
IN
–
Oil pressure switch status
–
–
–
OUT
–
–
–
–
IN
–
Washer fluid level sensor status
–
–
–
OUT
–
–
–
–
IN
–
Door lock status
–
–
–
OUT
–
IN
–
–
–
–
Torque down request
IN
OUT
–
–
–
–
–
–
–
–
ATF temperature
IN
OUT
–
–
–
–
–
–
–
–
ATX gear position/selector lever position
–
OUT
–
–
–
–
–
–
IN
–
Travelled distance
–
OUT
–
–
–
–
–
–
IN
–
Brake fluid pressure
–
IN
OUT
–
–
–
–
–
–
–
Torque down request
IN
–
OUT
–
–
–
–
–
–
–
Brake system status (EBD/ABS/DSC/RSC)
–
IN
OUT
–
–
–
–
–
–
–
IN
IN
OUT
–
–
–
–
–
–
–
IN
–
OUT
–
–
–
–
–
–
–
–
–
OUT
–
–
–
–
–
IN
–
Wheel speed (LF, RF, LR, RR)
IN
IN
OUT
IN
IN
IN
–
–
–
–
IN
IN
OUT
IN
IN
–
–
–
–
–
Brake system warning light on request
–
–
OUT
–
–
–
–
–
IN
–
ABS warning light on request
–
–
OUT
–
–
–
–
–
IN
–
Tire circumference (front/rear)
IN
–
OUT
–
–
–
–
–
–
–
DSC indicator light on request
–
–
OUT
–
–
–
–
–
IN
–
TCS OFF light on request
–
–
OUT
–
–
–
–
–
IN
–
Security light on request
–
–
–
–
–
–
–
OUT
IN
–
Keyless warning buzzer on request
–
–
–
–
–
–
–
OUT
IN
–
Keyless indicator light on request
–
–
–
–
–
–
–
OUT
IN
–
Keyless warning light on request
–
–
–
–
–
–
–
OUT
–
–
PLG operation request
–
–
–
–
–
IN
–
OUT
–
–
–
–
–
IN
–
OUT
–
–
–
–
–
–
–
IN
–
OUT
–
IN
IN
–
Buckle switch status
–
–
–
–
–
–
OUT
–
IN
–
Passenger sensing system status
–
–
–
–
–
–
OUT
–
IN
–
Air bag system warning light on request
–
–
–
–
–
–
OUT
–
IN
–
–
–
–
–
–
–
IN
–
OUT
–
Air bag system warning buzzer on status
–
–
–
–
–
–
OUT
–
IN
–
4WD system status
–
–
IN
–
OUT
–
–
–
–
–
–
–
–
–
OUT
–
–
–
IN
–
Fuel tank level
IN
–
–
–
–
–
–
–
OUT
IN
IN
–
–
–
–
–
–
–
OUT
–
Brake fluid level
–
–
IN
–
–
–
–
–
OUT
–
Parking brake switch status
IN
–
IN
–
IN
–
–
–
OUT
–
Ignition key position
IN
–
IN
–
–
–
–
–
OUT
–


CAN Signal-Chart (MS-CAN)

OUT: Output (sends signal)
IN: Input (receives signal)

Signal

Multiplex module

Audio unit

Audio amplifier

Information display
Audio status display request
OUT
–
IN
Ignition key position
OUT
–
IN
Drive information system data
OUT
–
IN
Buttons status
OUT
–
IN
Vehicle speed
OUT
IN
–
Audio system-related information
OUT
IN
–
IN
OUT
–
Beep sound request
IN
IN
OUT


On-Board Diagnostic Function

•  The on-board diagnostic function is incorporated into the following module:
―  PCM
―  TCM
―  DSC/RSC HU/CM
―  4WD control module
―  BCM
―  PLG control module
―  SAS control module
―  Keyless control module
―  Instrument cluster
―  Audio unit
―  Audio amplifier
―  Information display
―  Engine off natural vacuum (Engin-off-natural-vacuum is integrated in the PCM)
•  This function can narrow down CAN system malfunction locations.
•  The on-board diagnostic function consists of the following functions.
―  Failure detection function, which detects DTCs malfunctions in CAN system-related parts.
―  Memory function, which stores detected.
―  Self-malfunction diagnostic function, which indicates system malfunctions using DTCs and warning lights.
•  Using the Mazda Modular Diagnostic System (M-MDS), DTCs can be read out and deleted.
•  The CAN system has a fail-safe function. When a malfunction occurs in CAN system, the transmission module sends a warning signal and the receiving module illuminates the warning light.

Block diagram

HS-CAN

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MS-CAN

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Failure detection function

•  The failure detection function in each CAN system-related module detects malfunctions in input/output signals.
•  This function outputs the DTC for the detected malfunction to the DLC-2, and also sends the detected result to the memory function and fail-safe function.


Fail-safe function

•  When the failure detection function determines that there is a malfunction, the fail-safe function illuminates a warning light to inform the driver of the malfunction.


Memory function

•  The memory function stores the DTC for the malfunction of input/output signals for related parts, as determined by the failure detection function.


Self-malfunction diagnostic function

•  The self-malfunction diagnostic function determines that there is a malfunction, and outputs a signal, as a DTC, to the DLC-2. The DTC can be read out using the Mazda Modular Diagnostic System (M-MDS).

DTC table

DTC

Malfunction location

DTC output module
U0073
CAN system communication error
•  TCM
•  DSC/RSC HU/CM
•  BCM
•  4WD control module
•  PLG control module
•  SAS control module
•  Keyless control module
•  Instrument cluster
U0100
Communication error to PCM
•  TCM
•  DSC/RSC HU/CM
•  4WD control module
•  PLG control module
•  SAS control module
•  Keyless control module
•  Instrument cluster
U0101
Communication error to TCM
•  PCM
•  4WD control module
•  PLG control module
•  Instrument cluster
U0114
Communication error to 4WD control module
•  Instrument cluster
U0121
Communication error to DSC/RSC HU/CM
•  TCM
•  4WD control module
•  Instrument cluster
U0129
Communication error to DSC/RSC HU/CM
•  PCM
U0140
Communication error to BCM
•  TCM
•  DSC/RSC HU/CM
•  PLG control module
•  Keyless control module
•  Instrument cluster
U0151
Communication error to SAS control module
Instrument cluster
U0155
Communication error to instrument cluster
•  PCM
•  DSC/RSC HU/CM
•  4WD control module
•  PLG control module
•  SAS control module
U0184
Communication error to audio unit
Information display
U0214
Communication error to keyless control module
•  PLG control module
•  Instrument cluster
U0300
Internal control module software incompatibility
PCM
U0323
Communication error to instrument cluster
Keyless control module
U0415
Abnormal message from DSC/RSC HU/CM
TCM
U2023
Abnormal message from other modules
•  DSC/RSC HU/CM
•  Keyless control module
•  Instrument cluster
U2510
Communication error to PCM
Instrument cluster
U2516
CAN system communication error
Information display
23:Er11
Communication error to audio amplifier
Audio unit (Touch panel type)


Narrowing down malfunction locations

•  The on-board diagnostic function, by verifying the detected DTC information from each module, can narrow down a CAN system malfunction location. Refer to the self-malfunction diagnostic function for detailed information regarding DTCs. (See Self-malfunction diagnostic function.)

Flowchart

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Example (PCM-related communication error)

1.  DTCs for the PCM, DSC/RSC HU/CM and instrument cluster can be verified using the Mazda Modular Diagnostic System (M-MDS).

Module

Displayed DTC

Probable malfunction location
PCM
U0155
Communication error between PCM and instrument cluster
DSC/RSC HU/CM
–
–
Instrument cluster
U0100
Communication error between instrument cluster and PCM

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2.  If there is a communication error between the instrument cluster and PCM, even if the communication between the DSC/RSC HU/CM and the instrument cluster is normal, it is probable that there is a malfunction in the PCM or PCM-related wiring harnesses.