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 (ATX only)

DSC HU/CM

4WD control module

SAS control module

BCM

Keyless control module (with advanced keyless)

Instrument cluster

Immobilizer-related information
OUT
IN
IN
IN
OUT
IN
OUT
Engine torque
OUT
IN
Engine specification
OUT
IN
Brake pedal position
OUT
IN
Engine speed
OUT
IN
IN
IN
IN
Vehicle speed
OUT
IN
IN
IN
OUT
Throttle position
OUT
IN
IN
IN
Torque down request
IN
OUT
Tire circumference (front/rear)
OUT
IN
IN
IN
OUT
Engine coolant temperature
OUT
IN
IN
Intake air temperature
OUT
IN
MIL on request
OUT
IN
IN
OUT
Travelled distance
OUT
IN
IN
OUT
Fuel injection amount
OUT
IN
Generator warning light on request
OUT
IN
Cruise main/set indicator light on request
OUT
IN
Cruise control system-related information
OUT
IN
Target engine torque
IN
OUT
OUT
Target engine speed
IN
OUT
MTX gear position
OUT
IN
IN
IN
Shift lever position
OUT
IN
IN
ATX gear position
IN
OUT
IN
IN
IN
Selector lever position
IN
OUT
IN
IN
ATF temperature
IN
OUT
Brake system status (EBD/ABS/DSC)
IN
OUT
Brake system warning light on request
OUT
IN
ABS warning light on request
OUT
IN
DSC/TCS indicator light on request
OUT
IN
TCS OFF light on request
OUT
IN
Wheel speed (LF, RF, LR, RR)
IN
IN
OUT
IN
IN
4WD system status
IN
OUT
IN
Air bag system warning light on request
OUT
IN
Buckle switch status (driver-side, passenger-side)
OUT
IN
Passenger sensing system status
OUT
IN
Steering angle/steering angle sensor status
IN
OUT
Door switch status (LF, RF, LR, RR, liftgate)
OUT
IN
Door lock-link switch status (driver-side)
OUT
IN
Keyless indicator ligth on request
OUT
IN
Keyless warning ligth on request
OUT
IN
Keyless warning buzzer on request
OUT
IN
Key reminder switch status
OUT
IN
A/C on request
OUT
IN
IN
OUT
Turn indicator light on request
OUT
IN
Parking brake switch status
IN
OUT
IN
IN
OUT
Brake fluid level
OUT
IN
IN
OUT
Oil pressure switch status
OUT
IN
Door lock switch status
OUT
IN
Fuel tank level
IN
OUT
Security light on request
OUT
IN
Air bag system warning light status
IN
OUT


CAN Signal-Chart (MS-CAN)

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

Signal

Multiplex module

Information display

Climate control unit (with full-auto air conditioner)

Audio unit (base module)

Audio amplifier (with Bose®)

Instrument cluster

Beep sound request
OUT
IN
IN
INFO switch status
OUT
IN
IN
A/C on request
OUT
IN
A/C status display request
IN
OUT
Audio status display request
IN
OUT
Audio system-related information
OUT
IN
IN
OUT
Engine speed
IN
OUT
Vehicle speed
IN
IN
IN
OUT
Ignition key position
IN
IN
IN
OUT
Seat belt warning light status
IN
OUT
Dimmer switch status
IN
IN
OUT
Drive information system data
IN
OUT
Engine coolant temperature
IN
IN
OUT


On-Board Diagnostic Function

•  The on-board diagnostic function is incorporated into the following module:
―  PCM
―  TCM (ATX only)
―  DSC HU/CM
―  4WD control module
―  BCM
―  SAS control module
―  Keyless control module (with advanced kyeless)
―  Instrument cluster
―  Audio amplifier (with Bose®)
―  Climate control unit (with full-auto air conditioner)
―  Audio unit (base module)
―  Information display
•  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

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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

U0028
CAN system communication error
BCM
U0073
CAN system communication error
•  PCM
•  TCM (ATX only)
•  DSC HU/CM
•  4WD control module
•  BCM
•  SAS control module
•  Keyless control module (with advanced kyeless)
•  Instrument cluster
U0100
Communication error to PCM
•  TCM (ATX only)
•  DSC HU/CM
•  4WD control module
•  BCM
•  Keyless control module (with advanced kyeless)
•  Instrument cluster
U0101
Communication error to TCM (ATX only)
•  PCM
•  DSC HU/CM
•  4WD control module
•  Instrument cluster
U0114
Communication error to 4WD control module
•  DSC HU/CM
•  Instrument cluster
U0121
Communication error to DSC HU/CM
•  PCM
•  TCM (ATX only)
•  4WD control module
•  Instrument cluster
U0140
Communication error to BCM
•  DSC HU/CM
•  4WD control module (MTX only)
•  Keyless control module (with advanced kyeless)
•  Instrument cluster
Communication error to instrument cluster
TCM (ATX only)
U0151
Communication error to SAS control module
•  SAS control module
•  Instrument cluster
U0155
Communication error to instrument cluster
•  PCM
•  4WD control module
•  SAS control module
•  Climate control unit (with full-auto air conditioner)
U0164
Communication error to climate control unit (with full-auto air conditioner)
Instrument cluster
U0166
Communication error to climate control unit (with full-auto air conditioner)
Information display
U0181
Communication error to instrument cluster
Information display
U0184
Communication error to audio unit (base module)
Information display
U0323
Communication error to instrument cluster
Keyless control module (with advanced kyeless)
U0415
Abnormal message from DSC HU/CM
TCM (ATX only)
U0516
CAN system communication error
Climate control unit (with full-auto air conditioner)
U1900
Communication error to other module
DSC HU/CM
U2023
Abnormal message from PCM
•  DSC HU/CM
•  Keyless control module (with advanced kyeless)
•  Instrument cluster
U2516
CAN system communication error
•  Instrument cluster
•  Information display
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CAN system communication error
Audio unit (base module)


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 HU/CM and instrument cluster can be verified using the Mazda Modular Diagnostic System (M-MDS).

Module

Displayed DTC

Probable malfunction location

PCM
U0073
PCM-related CAN system malfunction
U0121
Communication error between PCM and DSC HU/CM
U0155
Communication error between PCM and instrument cluster
DSC HU/CM
U0100
Communication error between DSC HU/CM and PCM
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 HU/CM and the instrument cluster is normal, it is probable that there is a malfunction in the PCM or PCM-related wiring harnesses.