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 ll 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:
  Fig 1: Identifying Malfunction Indicator Lamp

  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. The emission control systems components.
2. The power train control components (which affect vehicle emissions).
3. The computer itself.

   In addition, the applicable DTCs prescribed by SAE J2012 are recorded in the ECM memory. If the malfunction does not recur in 3 consecutive trips, the MIL turns off automatically but the DTCs remain recorded in the ECM memory.

   To check the DTCs, connect Techstream to the DLC3. The Techstream displays DTCs, freeze frame data, and a variety of the engine data. The DTCs and freeze frame data can be erased with the Techstream. 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 simplification of 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).

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 15765-4 for communication protocol. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 15765-4 format.

Fig 2: Identifying DLC3 (Data Link Connector 3)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT: 

The DLC3 is the interface prepared for reading various data from the vehicle's ECM. After connecting the cable of Techstream, turn the engine switch on (IG) and turn the Techstream on. If a communication failure message is displayed on the Techstream screen (on the Techstream: UNABLE TO CONNECT TO VEHICLE), a problem exists in either the vehicle or Techstream. In order to identify the location of the problem, connect the Techstream to another vehicle.

• If communication is normal: Inspect the DLC3 on the original vehicle.
• If communication is still not possible: The problem is probably in the Techstream itself. Consult the Service Department listed in the instruction manual.

Standard Voltage

11 to 14 V

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

1. The MIL is illuminated when the engine 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 engine 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 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 engine switch on (IG).
3. Turn Techstream ON.
4. Clear the DTCs. Refer to DTC CHECK/CLEAR .
5. Perform the DTC judgment driving pattern to run the DTC judgment.
6. Enter 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
   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