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Diagnosis System

  1. DESCRIPTION 
    1. When troubleshooting on-Board Diagnostic (OBD II) vehicles, the vehicle must be connected to the OBD II scan tool (complying with SAE J1987). Various data output from the vehicle's ECM can then be read.
      Fig 1: Waveform Graph (Waveform 6)
      G05282628Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. OBD II regulations require that the vehicle's onboard computer illuminates the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in:
      1. The emission control system/components
      2. The power train control components (which affect vehicle emissions)
      3. The computer

        In addition, the applicable Diagnostic Trouble Codes (DTCs) prescribed by SAE J2012 are recorded in the ECM memory.

        If the malfunction does not reoccur in 3 consecutive trips, the MIL turns off automatically but the DTCs remain recorded in the ECM memory.

        Fig 2: Identifying (Mil) Malfunction Indicator Lamp
        G05282629Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    3. To check DTCs, connect the scan tool to the Data Link Connector 3 (DLC3) of the vehicle. The scan tool displays DTCs, the freeze frame data and a variety of the engine data.

      The DTCs and freeze frame data can be erased with the scan tool (see DTC CHECK / CLEAR  ).

  2. NORMAL MODE AND CHECK MODE 
    1. 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.
      Fig 3: Connecting Intelligent Tester To DLC3
      G05282630Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  3. TRIP DETECTION LOGIC 
    1. 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.
  4. FREEZE FRAME DATA 
    1. Freeze frame data records the engine conditions (fuel system, calculated load, engine coolant temperature, fuel trim, engine speed, vehicle speed, etc.) 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.
    2. The intelligent tester records freeze frame data in five different instances: 1) 3 times before the DTC is set, 2) once when the DTC is set, and 3) once after the DTC is set. These data can be used to simulate the vehicle's condition around the time when the malfunction occurred. The data may help find the cause of the malfunction, or judge if the DTC is being caused by a temporary malfunction or not.
      Fig 4: DTC Timing Chart
      G05282631Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  5. DATA LINK CONNECTOR 3 (DLC3) 
    1. 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 5: Identifying Data Link Connector 3 (DLC3)
      G05282632Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Terminal of DLC3 

      TERMINAL DESCRIPTION CHART

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

      If the result is not as specified, the DLC3 may have a malfunction. Repair or replace the harness and connector.

      HINT:

      Connect the cable of the intelligent tester to the DLC3, turn the ignition switch ON and attempt to use the tester. If the screen displays UNABLE TO CONNECT TO VEHICLE, a problem exists in the vehicle side or the tester side.

      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.

  6. CHECK MIL 
    1. Check that the MIL illuminates when turning the ignition switch ON.

      If the MIL does not illuminate, there is a problem in the MIL circuit (see MIL CIRCUIT ).

    2. When the engine is started, the MIL should turn off.
  7. ALL READINESS 
    1. For this vehicle, using the intelligent tester allows readiness codes corresponding to all DTCs to be read. When the diagnosis (normal or malfunctioning) has been completed, readiness codes are set. Enter the following menus:

      ENHANCED OBD II / MONITOR STATUS on the intelligent tester.

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