#
ON-BOARD DIAGNOSTIC FUNCTION

id094000101700

## Outline

• The on-board diagnostic function is incorporated into the PCM, ABS HU/CM, and instrument cluster. This function can narrow down CAN system malfunction locations.
• The on-board diagnostic function consists of the following functions: a failure detection function, which detects malfunctions in CAN system-related parts; a memory function, which stores detected DTCs; a self-malfunction diagnostic function, which indicates system malfunctions using DTCs and warning lights; and a PID/data monitoring function, which verifies the input/output condition of specific input/output signals being read out.
• Using a 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 advise the driver of the malfunction.

Module | Fail-safe function
--- | ---
PCM | • MIL illuminated
ABS HU/CM | • ABS suspended • ABS warning light illuminated
Instrument cluster | • Speedometer, tachometer, water temperature 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 a WDS or equivalent.

### DTC table

DTC | Malfunction location | DTC output module
--- | --- | ---
U0073 | CAN system communication error | PCM
U0121 | Communication error between the ABS HU/CM and DTC output unit
U0155 | Communication error between the instrument cluster and DTC output unit
U1900 | CAN system communication error | Instrument cluster
U2516 | CAN system wiring harness open or short circuit
U2523 | Communication error between the PCM and DTC output unit (Engine- related signal) | ABS HU/CM (Vehicles with ABS)

## 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 ABS HU/CM and instrument cluster.
• A WDS or equivalent is used to read out the PID/data monitor information.

PID name (definition) | WDS display | Detection state | PID monitor module | Terminal
--- | --- | --- | --- | ---
ABS_MSG (Signal reception error from the ABS HU/CM) | Present | Circuit between the ABS HU/CM and monitor module is normal. | Instrument cluster | Instrument cluster: 2W, 2X
Not Present | Circuit between the ABS HU/CM and monitor module is abnormal.
PCM_MSG (Signal reception error from PCM) | Present | Circuit between the PCM and monitor module is normal.
Not Present | Circuit between the PCM and monitor module is abnormal.

## Narrowing Down Malfunction Locations

• The on-board diagnostic function can narrow down a CAN system malfunction location by verifying the detected DTC and PID/data monitor information from each module. 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)

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

Module | Displayed DTC | Probable malfunction location
--- | --- | ---
PCM | U0073 | PCM-related CAN system malfunction
U0121 | Communication error between PCM and ABS HU/CM
U0155 | Communication error between PCM and instrument cluster
ABS HU/CM | U2523 | Communication error between PCM and ABS HU/CM
Instrument cluster | U1900, U2516 | Instrument cluster-related CAN system malfunction

2. PID/data monitor information for the instrument cluster can be verified using a 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 ABS HU/CM) | Present | Normal communication between instrument cluster and ABS HU/CM

3. If there is a communication error between the ABS HU/CM and PCM, or between the instrument cluster and PCM, even if the communication between the ABS HU/CM and the instrument cluster is normal, it is probable that there is a malfunction in the PCM or PCM-related wiring harnesses.