CAN SYSTEM DESCRIPTION

id094000101000

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.

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.

• 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.

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).

CAN Signal-Chart (HS-CAN)

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

Signal

Multiplex module

PCM

EHPAS control module

DSC HU/CM

Instrument cluster

ABS HU/CM

Engine speed
OUT
IN
IN
IN
Vehicle speed
OUT
IN
-
IN
ATX gear position/selector lever position (ATX)
OUT
IN
IN
IN
-
Neutral switch position (MTX)
OUT
IN
-
-
CPP switch position (MTX)
OUT
IN
-
-
Engine torque
OUT
-
IN
-
-
Throttle valve opening angle
OUT
-
IN
-
-
Brake pedal position
OUT
-
IN
-
Transaxle specifications
OUT
-
IN
-
-
TCC status (ATX)
OUT
-
IN
-

 

Engine specifications
OUT
-
IN
-
-
Immobilizer-related information
OUT
-
-
IN
IN
OUT
AT warning light on request (ATX)
OUT
-
-
IN
Engine coolant temperature
OUT
-
-
IN
Travelled distance
OUT
-
-
IN
Fuel injection amount
OUT
-
-
IN
MIL on request
OUT
-
-
IN
Generator warning light on request
OUT
-
-
IN
EHPAS control module malfunction
-
OUT
-
IN
Brake system status (EBD/ABS/DSC)
IN
-
OUT
-
Wheel speed (LF, RF, LR, RR)
IN
-
OUT
-
Brake system warning light on request
-
-
OUT
IN
ABS warning light on request
-
-
OUT
IN
DSC indicator light on request
-
-
OUT
IN
-
DSC OFF light on request
-
-
OUT
IN
-
Fuel tank level
IN
-
-
OUT
A/C on request
IN
-
-
OUT
Transaxle in reverse position
IN
-
-
OUT
Parking brake position
-
IN
-
OUT
Brake fluid level
-
-
-
OUT

CAN Signal-Chart (MS-CAN)

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

Signal

Multiplex module

Passenger junction box (PJB)

Climate control unit

SAS control module

Audio unit (base module)

Instrument cluster

Ambient temperature
OUT
IN
-
-
IN
-
IN
-
Front wiper status
OUT
IN
-
-
-
Turn indicator light on request
OUT
-
-
-
IN
Security light on request
OUT
-
-
-
IN
Alarm on request
OUT
-
-
-
IN
Each door status
OUT
-
-
-
IN
Brake fluid level
OUT
-
-
-
IN
High-beam indicator light on request
OUT
-
-
-
IN
Transaxle in reverse position
OUT
-
-
-
IN
Parking brake position
OUT
-
-
-
IN
Rear window defroster on request
IN
OUT
-
-
-
OUT
IN
A/C on request
IN
OUT
-
-
-
OUT
IN
A/C status display request
-
OUT
-
IN
-
Buckle switch status
-
-
OUT
-
IN
Air bag system warning light on request
-
-
OUT
-
IN
Seat belt warning light on request
-
-
OUT
-
IN
Seat belt warning alarm on request
-
-
OUT
-
IN
Air bag system warning alarm on request
-
-
OUT
-
IN
Temperature unit
-
IN
-
OUT
-
OUT
-
IN
INFO switch status
-
-
-
OUT
IN
Engine speed
IN
-
-
-
OUT
Vehicle speed
IN
IN
IN
IN
OUT
Engine coolant temperature
IN
IN
-
-
OUT
Key reminder switch position
IN
-
IN
-
OUT
Ignition key position
-
-
-
IN
OUT
Air bag system warning light status
-
-
IN
-
OUT
Drive information system data
-
-
-
IN
OUT

On-Board Diagnostic Function

• The on-board diagnostic function is incorporated into the following module:

- PCM
- ABS HU/CM (with ABS) or DSC HU/CM (with DSC)
- EHPAS control module
- Passenger junction box (PJB)
- Climate control unit
- SAS control module
- Audio unit (base module)
- Instrument cluster

• 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.
- PID/DATA monitoring function, which verifies the input/output condition of specific input/output signals being read out.

• Using the WDS or equivalent, DTCs can be read out and deleted, and the PID/DATA monitoring function can be activated.

• 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

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 WDS or equivalent.

DTC table

DTC

Malfunction location

DTC output module

U0073
CAN system communication error
• PCM
• EHPAS control module
• Instrument cluster
• SAS control module
U0100
Communication error to PCM
• EHPAS control module
• Instrument cluster
U0121
Communication error to DSC HU/CM or ABS HU/CM
• PCM
• Instrument cluster
U0131
Communication error to EHPAS control module
Instrument cluster
U0140
Communication error to PJB
• Instrument cluster
• Climate control unit
U0151
Communication error to SAS control module
Instrument cluster
U0155
Communication error to instrument cluster
• PCM
• Climate control unit
U0184
Communication error to audio unit (base module)
• Instrument cluster
• Climate control unit
U0516
CAN system communication error
Climate control unit
U1900
Communication error to instrument cluster
• ABS HU/CM (with ABS)
• DSC HU/CM (with DSC)
• SAS control module
CAN system communication error
Abnormal message
PJB
U2012
CAN system communication error
• ABS HU/CM (with ABS)
• DSC HU/CM (with DSC)
U2023
Abnormal message from PCM
EHPAS control module
U2202
Communication error to PCM
ABS HU/CM
U2516
CAN system communication error
Instrument cluster
U2523
Communication error to PCM
• ABS HU/CM (with ABS)
• DSC HU/CM (with DSC)

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

Example (PCM-related communication error)

Note
• This example is for Z6 with DSC.

1. DTCs for the PCM, DSC HU/CM and instrument cluster can be verified using the WDS or equivalent.

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
U2523
Communication error between DSC HU/CM and PCM
Instrument cluster
U0100
Communication error between instrument cluster and PCM

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.