Diagnosis System

When troubleshooting On-Board Diagnostics (OBD II) vehicles, the Techstream (complying with SAE J1987) must be connected to the Data Link Connector 3 (DLC3) of the vehicle. Various data in the vehicle's Engine Control Module (ECM) can then be read OBD II regulations require that the vehicle's on-board computer illuminate the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in:

1. The emission control systems 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, the applicable Diagnostic Trouble Codes (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 the 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 DIAGNOSTIC TROUBLE CODE CHART  ) In order to enhance OBD function on vehicles and develop the Off-Board diagnosis system, the Control Area Network (CAN) communication is used 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 that span multiple ECUs and sensors. It allows high speed communication between the systems and simplifies the wire harness connections. The Techstream and ECM uses CAN communication signals to communicate.

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).

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 Data Link Connector 3

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:

Connect the cable of the Techstream to the DLC3, turn the ignition switch ON and attempt to use the tester. If the display indicates that a communication error has occurred, there is a problem either with the vehicle or with the tester.

If communication is normal when the tester is connected to another vehicle, inspect the DLC3 of the original vehicle.

If communication is still not possible when the tester is connected to another vehicle, the problem may be in the tester itself. Consult the Service Department listed in the tester's instruction manual.

Battery voltage: 

11 to 14 V 

If the voltage is below 11 V, recharge or replace 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 the Techstream.
• You should check "All Readiness" after simulating malfunction symptoms or for validation after finishing repairs.

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch ON.
3. Turn the tester ON.
4. Clear the DTCs.
5. Perform the DTC judgment driving pattern to run the DTC judgment.
6. Enter the following menus: Powertrain/Engine and ECT/Utility/All Readiness.
7. Input the DTCs to be confirmed.
8. Check the DTC judgment result.
   TESTER DISPLAY DESCRIPTION
   
   

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