Diagnosis System

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

Fig 1: Identifying Malfunction Indicator Lamp

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

• OBD II regulations require that the vehicle's on-board computer illuminates the MIL (Malfunction Indicator Lamp) on the instrument panel when the computer detects a malfunction in:
  1. The emission control systems and components
  2. The power train 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.
• To check DTCs, connect the Techstream to the DLC3. The Techstream displays DTCs, freeze frame data, and a variety of engine data. The DTCs and freeze frame data can be erased with the Techstream. Refer to DTC CHECK / CLEAR .
• In order to enhance OBD function on vehicles and develop the Off-Board diagnosis system, CAN communication is introduced in this system (CAN: Controller Area Network). It minimizes a gap between technician skills and vehicle technology. CAN is a network, which uses a pair of data transmission lines, spanning multiple computers and sensors. It allows a high speed communication between the systems and to simplify the wire harness connection.

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 (Techstream only). Refer to CHECK FOR INTERMITTENT PROBLEMS .

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).

Freeze frame data record the engine condition (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.

Check the DLC3. Refer to GENERAL INFORMATION .

Standard Voltage

11 to 14 V

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

1. The MIL is illuminated when the ignition switch is first turned ON (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 ignition switch is first turned ON, check the MIL circuit. Refer to MIL Circuit .

HINT: 

With All Readiness you can check whether or not the DTC judgment has been completed by using the Techstream.

You should check All Readiness after simulating malfunction symptoms or for validation after finishing repairs.

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON and turn the Techstream on.
7. Perform the DTC judgment driving pattern to run the DTC judgment.
8. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
9. Input the DTCs to be confirmed.
10. Check the DTC judgment result.

    Tester Display	Description
    NORMAL	DTC judgment completed System normal
    ABNORMAL	DTC judgment completed System abnormal
    INCOMPLETE	DTC judgment not completed You should perform driving pattern after confirming DTC enabling conditions
    UNKNOWN	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU's memory limit