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Diagnosis System

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  1. DESCRIPTION 
    1. When troubleshooting OBD II vehicles, the only difference from the usual troubleshooting procedure is to connect a Techstream (complying with SAE J1987) to the vehicle, and read off various data output by the vehicle's ECM.
    2. OBD II regulations require that the vehicle's onboard computer illuminate the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in the computer itself or in the drive system components which affect the vehicle emissions. In addition to illuminating the MIL when a malfunction is detected, the applicable DTCs prescribed by SAE J2012 are recorded in the ECM memory (See DIAGNOSTIC TROUBLE CODE CHART  ).

      If the malfunction does not occur in 3 consecutive trips, the MIL goes off but the DTCs remain in the ECM memory.

      Fig 1: Identifying Malfunction Indicator Lamp (MIL)
      G04828032Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    3. To check the DTCs, connect the Techstream to the DLC3 of the vehicle. The Techstream also enables you to erase the DTCs and check freeze frame data and various forms of engine data (For operating instructions, see the instruction book ).
    4. The DTCs include SAE controlled codes and manufacturer controlled codes. SAE controlled codes must be set as prescribed by the SAE, while manufacturer controlled codes can be set freely by the manufacturer within the prescribed limits (See DIAGNOSTIC TROUBLE CODE CHART  ).
    5. 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.
    6. 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 turned to ON again, and same malfunction is detected again, the MIL illuminates.
    7. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
    8. The Techstream displays freeze frame data recorded at five different points: 1) 3 times before the DTC is set, 2) once when the DTC is set, and 3) once after the DTC is set. The data can be used to simulate the vehicle's condition around the time of the malfunction. The data may be helpful in determining the cause of a malfunction. It may also be helpful in determining whether a DTC is being caused by a temporary malfunction.
      Fig 2: Identifying Freeze Frame Data
      G05590901Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  2. INSPECT DLC3 
    1. The ECM uses ISO 15765-4 for communication. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 15765-4 format.
      Fig 3: Identifying DLC3 Connector Terminals
      G04831026Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      CONNECTOR TERMINAL REFERENCE

      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 11 to 14 V
      CANH (6) - CANL (14) CAN bus line Ignition switch OFF(1) 54 to 69 Ω
      CANH (6) - CG (4) HIGH-level CAN bus line Ignition switch OFF(1) 200 Ω or higher
      CANL (14) - CG (4) LOW-level CAN bus line Ignition switch OFF(1) 200 Ω or higher
      CANH (6) - BAT (16) HIGH-level CAN bus line Ignition switch OFF(1) 6 kΩ or higher
      CANL (14) - BAT (16) LOW-level CAN bus line Ignition switch OFF(1) 6 kΩ 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.

    2. Connect the cable of the Techstream to the DLC3, turn the ignition switch to 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 with the tester.

      HINT:

      • If the communication is normal when the tester is connected to another vehicle, inspect the DLC3 on the original vehicle.
      • If the communication is still impossible 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.
  3. CHECK BATTERY VOLTAGE 
    1. Measure the battery voltage.

      Standard voltage: 

      11 to 14 V 

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

  4. CHECK MIL 
    1. The MIL comes on when the ignition switch is turned to ON and the engine is not running.

      HINT:

      If the MIL does not light up, troubleshoot the combination meter.

    2. When the engine is started, the MIL should go off. If the lamp remains on, it means that the diagnosis system has detected a malfunction or abnormality in the system.
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