CAN SYSTEM DESCRIPTION


BHE094055430T04

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.

1
Input signal
2
Output signal
3
Connector
4
Input interface
5
Output interface
6
CPU
7
Conventional module
8
Can harness (twisted pair)
9
Conventional wiring harness
10
Maltiplex block
11
Computation processing block
12
Can system-related module

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.

1
CAN_H
2
CAN_L

• 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.

1
Non-multiplex system
2
Time division multiplex system
3
Data
4
OFF
5
ON
6
Each signal is transmitted one by one through the channel as it is received.
7
Each signal is output one by one as it is received from the channel.

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).

1
Conventional system
2
Electrical module
3
CAN system
4
CAN system-related module

CAN Signal-Chart

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

Signal

Multiplex module

PCM

EPS control module

Keyless unit

TCM (AT)

DSC HU/CM

Steering angle sensor

Instrument cluster

Immobilizer-related information
OUT
-
IN
-
-
-
-
IN
-
OUT
-
-
-
-
Engine speed
OUT
IN
IN
IN
IN
-
IN
Vehicle speed
OUT
IN
-
-
-
-
IN
IN
-
-
OUT
-
-
-
Throttle valve opening angle
OUT
-
-
IN
IN
-
-
Engine coolant temperature
OUT
-
-
IN
-
-
IN
Engine torque
OUT
-
-
IN
IN
-
IN
Torque reduction disabled
OUT
-
-
IN
IN
-
-
Travelled distance
OUT
-
-
-
-
-
IN
-
-
-
-
OUT
-
IN
Fuel injection amount
OUT
-
-
-
-
-
IN
Engine oil pressure
OUT
-
-
-
-
-
IN
Engine oil level
OUT
-
-
-
-
-
IN
Engine coolant level
OUT
-
-
-
-
-
IN
Fuel pump status
OUT
-
-
-
-
-
IN
MIL on request
OUT
-
-
-
-
-
IN
IN
-
-
OUT
-
-
-
Generator warning light on request
OUT
-
-
-
-
-
IN
Transmission/axle specifications
OUT
-
-
-
IN
-
-
Tire size
OUT
-
-
-
IN
-
-
Cruise control main indicator light on request
OUT
-
-
IN
-
-
IN
Cruise control indicator light on request
OUT
-
-
IN
-
-
IN
Downshift request
OUT
-
-
IN
-
-
-
EPS warning light on request
-
OUT
-
-
-
-
IN
Idle speed increase request
IN
OUT
-
OUT
-
-
-
Ignition switch off time
IN
-
OUT
-
-
-
-
Target torque
IN
-
-
OUT
-
-
-
Torque upper limit
IN
-
-
OUT
-
-
-
Turbine shaft speed
IN
-
-
OUT
-
-
-
Target gear position/selector lever position
IN
-
-
OUT
IN
-
IN
Gear ratio
IN
-
-
OUT
-
-
-
Brake system status (EBD/ABS/DSC)
IN
IN
-
IN
OUT
-
IN
Torque reduction request
IN
-
-
OUT
OUT
-
-
Wheel speed (LF, RF, LR, RR)
IN
-
-
-
OUT
-
-
Wheel speed status (LF, RF, LR, RR)
IN
-
-
-
OUT
-
-
Steering angle
-
-
-
-
IN
OUT
-
Steering angle sensor status (sensor malfunction, circuit malfunction)
-
-
-
-
IN
OUT
-
Fuel tank level
IN
-
-
-
-
-
OUT
Parking brake position
-
-
-
-
IN
-
OUT
AT warning light on request
-
-
-
OUT
-
-
IN

On-Board Diagnostic Function

• The on-board diagnostic function is incorporated into the PCM, TCM, DSC HU/CM, keyless unit, EPS control module and 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

1
PCM
2
EPS control module
3
AT
4
TCM
5
Steering angle sensor
6
Twisted pair
7
DSC HU/CM
8
Keyless unit
9
DLC-2
10
Instrument cluster
11
CAN_H
12
CAN_L

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.

Module

Fail-safe function

PCM
• MIL illuminated
EPS control module
• EPS warning light illuminated
Keyless unit
-
TCM
• AT warning light illuminated
DSC HU/CM
• ABS suspended
• TCS suspended
• DSC suspended
• ABS warning light illuminated
• DSC indicator light illuminated
• DSC OFF light illuminated
Steering angle sensor
• Send malfunction data to DSC HU/CM
Instrument cluster
• Speedometer, tachometer, water temperature gauge, oil pressure gauge: 0 displayed

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
• TCM
• EPS control module
• Keyless unit
U0100
Communication error to PCM
TCM
U0101
Communication error to TCM
PCM
U0121
Communication error to DSC HU/CM
PCM
U0155
Communication error to instrument cluster
U2510
Communication error to PCM
Keyless unit
U1147
U1900
CAN system communication error
• DSC HU/CM
• EPS control module
• Steering angle sensor
• Keyless unit
• Instrument cluster
U2516
CAN system wiring harness open or short circuit
• DSC HU/CM
• Steering angle sensor
• Instrument cluster

PID/DATA monitoring function

• The PID/DATA monitoring function is used to freely select and read out, in real time, the monitored items for the input/output signals of the instrument cluster.
• The WDS or equivalent is used to read out the PID/DATA monitor information.

PID name (definition)

Condition

Specification

PID monitor module

Terminal

ABS_MSG
(Missing message from the DSC HU/CM)
Present
Circuit in the DSC HU/CM is normal
Instrument cluster
• DSC HU/CM: H, I
• Instrument cluster: 1J, 1L
Not Present
Circuit in the DSC HU/CM is disable
TCM_MSG
(Missing message from the TCM)
Present
Circuit in the TCM is normal
• TCM: 1V, 1Y
• Instrument cluster: 1J, 1L
Not Present
Circuit in the TCM is disable
EPS_MSG
(Missing message from the EPS control module)
Present
Circuit in the EPS control module is normal
• EPS control module: 2K, 2M
• Instrument cluster: 1J, 1L
Not Present
Circuit in the EPS control module is disable
PCM_MSG
(Missing message from the PCM)
Present
Circuit in the PCM is normal
• PCM: 4S, 4V
• Instrument cluster: 1J, 1L
Not Present
Circuit in the PCM is disable

Narrowing down malfunction locations

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

Flowchart

Example (PCM-related communication error)

Note
• This example is for MT 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
U1900, U2516
DSC HU/CM-related CAN system malfunction
Instrument cluster
U1900, U2516
Instrument cluster-related CAN system malfunction

1
PCM
2
DLC-2
3
Instrument cluster
4
DSC HU/CM
5
Twisted pair

2.  PID/DATA monitor information for the instrument cluster can be verified using the WDS or equivalent.

Module

PID name (definition)

Condition

Probable malfunction point

Instrument cluster
PCM_MSG
(Missing message from the PCM)
Not Present
Communication error between instrument cluster and PCM
ABS_MSG
(Missing message from the DSC HU/CM)
Present
Normal communication between instrument cluster and DSC HU/CM

1
PCM
2
DLC-2
3
Instrument cluster
4
DSC HU/CM
5
Twisted pair

3. 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.