Diagnosis System

• When troubleshooting OBD II (On-Board Diagnostics) vehicles, 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.
• 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 Techstream to the DLC3. Techstream displays DTCs, freeze frame data, and a variety of engine data. The DTCs and freeze frame data can be erased with Techstream (See DTC CHECK / CLEAR  ).
     Fig 1: Identifying Malfunction Indicator Lamp

     Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

The diagnosis system operates in the 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) (See CHECK MODE PROCEDURE  ).

Fig 2: Identifying DLC3 Connector Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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).

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.

The vehicle's ECM uses the ISO 9141-2 communication protocol. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 9141-2 format.

Fig 3: Identifying DLC3 Connector Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

If the result is not as specified, the DLC3 may have a malfunction.

Repair or replace harness or connector.

If the CAN communication has a malfunction, proceed to CAN communication troubleshooting (See HOW TO PROCEED WITH TROUBLESHOOTING ).

HINT:

• The DLC3 is the interface prepared for reading various data from the vehicle's ECM. After connecting the cable of Techstream, turn the ignition switch to the ON position and turn the tester on.
• If a communication failure message is displayed on the Techstream screen a problem exists in either the vehicle or tester. In order to identify the location of the problem, connect the tester to another vehicle.
• If communication is normal: Inspect the DLC3 on the original vehicle.
• If communication is impossible: The problem is probably with the tester itself. Consult the Service Department listed in the instruction manual.

Battery Voltage: 11 to 14 V 

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

1. The MIL is illuminated when the ignition switch is first turned to the ON position (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 to the ON position, check the MIL circuit (See MIL CIRCUIT  ).

HINT:

• With All Readiness you can check whether or not the DTC judgment has been completed by using Techstream.
• You should check All Readiness after simulating malfunction symptoms or for validation after finishing repairs.

1. Connect Techstream to the DLC3.
2. Turn the ignition switch to the ON position.
3. Turn Techstream on.
4. Clear the DTCs (See DTC CHECK / CLEAR  ).
5. Perform the DTC judgment driving pattern to run the DTC judgment.
6. Select the following menu items: Powertrain / Engine / Utility / All Readiness.
7. Input the DTCs to be confirmed.
8. Check the DTC judgment result.

   Techstream: 

   TESTER DISPLAY DESCRIPTION
   
   

   Tester Display	Description
   NORMAL	DTC judgment completed System normal
   ABNORMAL	DTC judgment completed System normal
   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