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Diagnosis System

  1. DESCRIPTION 

    When troubleshooting On-Board Diagnostics (OBD II) vehicles, the intelligent tester (complying with SAE J1987) must be connected to the Data Link Connector 3 (DLC3) of the vehicle. Various data in the vehicle's Engine Control Module (ECM) can then be read.

    OBD II regulations require that the vehicle's on-board computer illuminates the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in:

    1. The emission control systems components
    2. The powertrain control components (which affect vehicle emissions)
    3. The computer itself

    In addition, the applicable DTCs (Diagnostic Trouble Codes) prescribed by SAE J2012 are recorded on 3 consecutive trips, the MIL turns off automatically but the DTCs remain recorded in the ECM memory.

    Fig 1: Identifying (Mil) Malfunction Indicator Lamp
    G04828032Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    To check the DTCs, connect the intelligent tester to the DLC3. The tester displays DTCs, freeze frame data, and a variety of engine data. The DTCs and freeze frame data can be erased with the tester. In order to enhance OBD function on vehicles and develop the Off-Board diagnosis system, the Control Area Network (CAN) communication is used in this system. It minimizes the gap between technician skills and vehicle technology. CAN is a network, which uses a pair of data transmission lines that span multiple ECUs and sensors. It allows high speed communication between the systems and simplifies the wire harness connections. The CAN Vehicle Interface Module (CAN VIM) must be connected with the intelligent tester to display any information from the ECM. The intelligent tester and ECM uses CAN communication signals to communicate. Connect the CAN VIM between the intelligent tester and DLC3.

    Fig 2: Connecting Intelligent Tester To DLC3
    G05285449Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  2. 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 as an option for technicians. In check mode, 1 trip detection logic is used for simulating malfunction symptoms and increasing the system's ability to detect malfunctions, including intermittent problems (intelligent tester only).

  3. TRIP DETECTION LOGIC 

    When a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip). If the same malfunction is detected during the next subsequent drive cycle, the MIL is illuminated (2nd trip).

  4. FREEZE FRAME DATA 

    Freeze frame data records the engine conditions (fuel system, calculated engine load, engine coolant temperature, fuel trim, engine speed, vehicle speed, etc.) when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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.

  5. Data link Connector 3 (DLC3) 

    The vehicle's ECM uses the ISO 15765-4 for communication protocol. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 15765-4 format.

    Fig 3: Identifying DLC3 Connector Terminals
    G04967779Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    TERMINAL DESCRIPTION SPECIFIED CONDITION CHART

    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 μ
    SG (5) - Body ground Signal ground Always Below 1 μ
    BAT (16) - Body ground Battery positive Always 9 to 14 V
    CANH (6) - CANL (14) CAN bus line Engine switch off(1) 54 to 69 μ
    CANH (6) - Battery positive HIGH-level CAN bus line Engine switch off(1) 6 kΩ or higher
    CANH (6) - CG (4) HIGH-level CAN bus line Engine switch off(1) 200 Ω or higher
    CANL (14) - Battery positive LOW-level CAN bus line Engine switch off(1) 6 kΩ or higher
    CANL (14) - CG (4) LOW-level CAN bus line Engine switch off(1) 200 Ω or higher
    NOTE:
    (1) Before measuring the resistance, leave the vehicle as is for at least 1 minute and do not operate the engine switch, any other switches or the doors.

    HINT:

    Connect the cable of the intelligent tester to the DLC3, turn the engine switch on (IG) 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 with the tester.

    If communication is normal when the tester is connected to another vehicle, inspect the DLC3 of the original vehicle.

    If communication is still not possible when the tester is connected to another vehicle, the problem may be in the tester itself. Consult the Service Department listed in the tester's instruction manual.

  6. BATTERY VOLTAGE 

    Battery voltage: 

    11 to 14 V 

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

  7. Malfunction Indicator Lamp (MIL) 
    1. The MIL is illuminated when the engine switch is first turned on (IG) (the engine is not running).
    2. The MIL should turn OFF when the engine is started. If the MIL remains illuminated, the diagnosis system has detected a malfunction or abnormality in the system.

    HINT:

    If the MIL is not illuminated when the engine switch is first turned on (IG), check the MIL CIRCUIT .

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