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 illuminate the MIL (Malfunction Indicator Lamp) on the instrument panel when the computer detects a malfunction in:

1. The emission control system components.
2. The powertrain control components (which affect vehicle emissions).
3. The computer itself.
   Fig 1: Identifying Malfunction Indicator Lamp

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

In addition, if the applicable DTCs (Diagnostic Trouble Codes) prescribed by SAE J2012 are not 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. 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 (see DTC CHECK / CLEAR  ).

In order to enhance OBD function on vehicles and develop the Off-Board diagnosis system, CAN (Controller Area Network) communication is introduced in this system. It minimizes the 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 high speed communication between the systems and simplifies 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) (see CHECK MODE PROCEDURE  ).

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 records the engine conditions (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.

Fig 2: 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 the harness and connector.

HINT:

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 article.

Standard battery voltage: 

11 to 14 V 

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

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 (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 ON.
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 and ECT / 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