Diagnosis System

1. 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.
2. OBD II regulations require that the vehicle's onboard 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.

      Fig 1: Identifying Malfunction Indicator Lamp

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. To check for DTCs, connect Techstream 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 (See FREEZE FRAME DATA  ).

   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.

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 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  ).

1. 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).
   Fig 2: Identifying DLC3 Connector Terminals

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. 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.

1. Check DLC3 (See HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS ).

Battery Voltage: 11 to 14 V 

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

1. The MIL is illuminated when turned the ignition switch 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 turned the ignition switch on (IG), check 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 on (IG).
3. Turn the tester 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.