SFI SYSTEM > DIAGNOSIS SYSTEM

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DESCRIPTION FOR M-OBD

When troubleshooting Multiplex OBD (M-OBD) vehicles, the vehicle must be connected to the intelligent tester. Various data output from the vehicle's Engine Control Module (ECM) can then be read.
The Malfunction Indicator Lamp (MIL) is illuminated when the vehicle's onboard computer detects a malfunction in the computer itself or in drive system components. In addition, the applicable Diagnostic Trouble Codes (DTCs) are recorded in the ECM memory (Click here).
If the malfunction does not reoccur, the MIL stays illuminated until the ignition switch is turned OFF, and then the MIL turns OFF when the ignition switch is turned ON. However, the DTCs remain recorded in the ECM memory.
To check the DTCs, connect the intelligent tester to the Data Link Connector 3 (DLC3) on the vehicle, or connect terminals TC and CG on the DLC3 (DTCs will be displayed on the combination meter).

NORMAL MODE AND CHECK MODE

The diagnosis system operates in "normal mode" during normal vehicle use. In normal mode, 2 trip detection logic is used to ensure accurate detection of malfunctions. "Check mode" is also available to technicians as an option. In check mode, 1 trip detection logic is used for simulating malfunction symptoms and increasing the system's ability to detect malfunctions, including intermittent malfunctions (Click here).

2 TRIP DETECTION LOGIC

When a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip). If the ignition switch is turned OFF and then ON again, and the same malfunction is detected again, the MIL will illuminate (2nd trip).

FREEZE FRAME DATA

Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.

CHECK DLC3

The vehicle's ECM uses the ISO 14230 (M-OBD) communication protocol. The terminal arrangement of the DLC3 complies with ISO 15031-03 and matches the ISO 14230 format.
If the result is not as specified, the DLC3 may have a malfunction. Repair or replace the harness and connector.

Symbol (Terminal No.)	Terminal Description	Condition	Specified Condition
SIL (7) - SG (5)	Bus "+" line	During transmission	Pulse generation
CG (4) - Body ground	Chassis ground	Always	Below 1 Ω
SG (4) - Body ground	Signal ground	Always	Below 1 Ω
BATT (16) - Body ground	Battery positive	Always	9 to 14 V

HINT:

Connect the cable of the intelligent tester to the DLC3, turn the ignition switch ON and attempt to use the tester. If the display indicates that a communication error has occurred, there is a problem either with the vehicle or withe the tester.

If communication is normal when the tester is connected to another vehicle, inspect the DLC3 on the original vehicle.
If communication is still not possible when the tester is connected to another vehicle, the problem is probably in the tester itself. Consult the Service Department listed in the tester's instruction manual.

INSPECT BATTERY VOLTAGE

If voltage is below 11 V, recharge or replace the battery before proceeding.

Battery Voltage:: 11 to 14 V

CHECK MIL

The MIL illuminates when the ignition switch is turned ON and the engine is not running.
HINT:
If the MIL does not illuminate, troubleshooting the MIL circuit (Click here).
When the engine is started, the MIL should turn off. If the MIL remains illuminated, the diagnosis system has detected a malfunction or abnormality in the system.