CAN SYSTEM DESCRIPTION

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.

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

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

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 • 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.

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.

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

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.