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 (included in the hybrid vehicle control ECU) 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:

Fig 1: Identifying (MIL) Malfunction Indicator Lamp

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. The emission control system components.
2. The powertrain 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 (included in the hybrid vehicle control ECU) memory. To check for DTCs, connect Techstream to the DLC3. The tester displays DTCs, freeze frame data, and a variety of the engine data. The DTCs and freeze frame data can be erased with the tester. In order to enhance OBD function on vehicles and develop the On-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 (included in the hybrid vehicle control ECU) memory (1st trip). If the same malfunction is detected during the next subsequent drive cycle, the MIL is illuminates (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 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 Terminal

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

The DLC3 is the interface prepared for reading various data from the vehicle's ECM (included in the hybrid vehicle control ECU). After connecting the of Techstream cable, turn the power switch on (IG) and turn the tester on. If a communication failure message is displayed on the tester 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 still not possible: The problem is probably in the tester itself. Consult the Service Department listed in the instruction manual.

Auxiliary battery voltage: 

11 to 14 V 

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

1. The MIL is illuminated when the power 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 malfunctions or abnormalities in the system.

   HINT:

   If the MIL is not illuminated when the power switch is first turned on, check the 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 power 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.