MULTIPLEX COMMUNICATION SYSTEM CONSTRUCTION/OPERATION [L3]

CAN System-Related Module Construction

• A CAN system-related module is composed of a power circuit, CPU, and input/output interface.

• Module size has been reduced due to the elimination of redundant parts of the input/output interface used in conventional types of electronic modules.

• The CPU (multiplex block) controls all signals exchanged via the bus lines (multiplex communication system wiring harnesses).

• Communication with non-multiplex parts is carried out using conventional input/output interface.

• The functions of each component are shown below.

Twisted Pair Construction

• The CAN system uses two spirally twisted wires called a twisted pair, and each wire, bus line A (CAN_L) and bus line B (CAN_H), has unique characteristics.

• Both bus lines are opposite phase voltage so that emitted noise is lessened and exterior noise interference is not easily received.

CAN System Outline

• For information exchange between electronic modules in a conventional system, separate information signals are required. However, with the CAN system, it is possible to send a large amount of information via a small wiring harness by sending multiple signals at varying times over one channel. This is referred to as time division multiplexing.

CAN System Operation

Time Division Multiplex

• 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 connected and electricity must flow through each transmission channel.

• With the time multiplex system, this can be done through a single wire. 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 are illuminated.

Vehicle CAN System

• By rearranging the multiple signal, common information between the electronic modules is transmitted and received via the twisted pairs.

• The signal transmitted by one CAN system-related module is sent via twisted pairs to all the CAN system-related modules, but only the corresponding module(s) receives the signal and performs the appropriate operation.

CAN Signal Table

• Sending/receiving of CAN signals is as follows:

ON-BOARD DIAGNOSTIC SYSTEM OUTLINE

• CAN system-related modules have an on-board diagnostic function that is able to determine malfunction locations when there is an irregularity in the CAN system.

• The on-board diagnostic function has a malfunction detection function that detects irregularities in CAN system-related parts, a memory function that stores detected malfunctions, and a display function that displays the location and contents of malfunctions via DTC output.

• DTCs can be read out and cleared using the WDS or equivalent.

• The CAN system has a fail-safe function. When a malfunction occurs in the CAN system, the transmission module sends a warning signal, the receiving module illuminates the warning light, and the fail-safe function performs control to safeguard the system.

On-Board Diagnostic System Construction/Operation

Block Diagram

Malfunction detection function

• Detects irregularities in the input/output signals of CAN system-related modules.

• The DTC for the detected malfunction is output to the DLC-2, and the detected result is also sent to the memory, display, and fail-safe functions.

Fail-safe function

• When the malfunction detection function determines that there is an irregularity, the fail-safe function illuminates a warning light to advise the driver and controls input and output parts to allow safe driving.

Memory function

• Stores DTCs for malfunctions of the input/output signal system, as determined by the malfunction detection function.

Display function

• Outputs the signal for a malfunction determined by the malfunction detection function as a DTC to the DLC-2.

• DTCs can be read out using the WDS or equivalent.

DTC table

DTC	Malfunction location	DTC Output Unit
U0073	Module communication error	• PCM • Instrument cluster
U0121	Communication error	PCM
U1900	Communication error	• ABS HU/CM • Instrument cluster
U2023	Abnormal data	ABS HU/CM

PID/data monitor function

• The PID/data monitor function is used for optionally selecting input/output signal monitor items preset in the instrument cluster and reading them out in real-time.

• PIDs can be read out using the WDS or equivalent.

Malfunction Location Determination

• The on-board diagnostic function can determine CAN system malfunction locations by verifying the detected DTC information from each module.

• Refer to the display function for a detailed explanation of DTCs. (See Display function.)

Example (PCM-related wiring harness open circuit)

Note

• This example applies to the PCM, ABS HU/CM, and instrument cluster.

1. DTCs for CAN system-related modules are verified using the WDS or equivalent.

2. Instrument cluster PIDs are 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.