Diagnosis System

1. When troubleshooting On-Board Diagnostic (OBD II) vehicles, the vehicle must be connected to Techstream. Various data output from the vehicle's TCM can be read then.
2. 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:
   Fig 1: Identifying Malfunction Indicator Lamp

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. The emission control system/components
   2. The power train control components (which affect vehicle emissions)
   3. The computer

      In addition, the applicable Diagnostic Trouble Codes (DTCs) prescribed by SAE J2012 are recorded in the TCM memory.

      If the malfunction does not reoccur in 3 consecutive trips, the MIL turns off automatically but the DTCs remain recorded in the TCM memory.

3. To check DTCs, connect Techstream to the Data Link Connector 3 (DLC3) of the vehicle. The Techstream displays DTCs, the freeze frame data and a variety of the engine data.

   The DTCs and freeze frame data can be erased with Techstream. Refer to DTC CHECK / CLEAR .

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 to technicians as an option. In check mode, "1 trip detection logic" is used for simulating malfunction symptoms and increasing the system's ability to detect malfunctions, including intermittent malfunctions.

1. When a malfunction is first detected, the malfunction is temporarily stored in the TCM memory (1st trip). If the ignition switch is turned off and then on (IG) again, and the same malfunction is detected again, the MIL will illuminate.

1. The TCM 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.
2. The Techstream displays freeze frame data recorded at five different points: 1) 3 points before the DTC is set, 2) once when the DTC is set, and 3) once after the DTC is set. The data can be used to simulate the vehicle's condition around the time of the malfunction. The data may be helpful in determining the cause of a malfunction. It may also be helpful in determining whether a DTC is being caused by a temporary malfunction.
   Fig 2: Identifying Freeze Frame Data

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. The vehicle's TCM 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 3: Identifying DLC3 Connector Terminals

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   HINT: 

   Connect the cable of Techstream to the DLC3, turn the ignition switch on (IG) and attempt to use Techstream. If the screen displays a communication error message, a problem exists in the vehicle side or the tester side.

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

   If the communication is still impossible when the tester is connected to another vehicle, the problem is probably in the tester itself. Consult the Service Department listed in the tester's instruction manual.

   Terminals of DLC 3

   Terminal No.	Symbol	Name	Reference Terminal	Result	Condition
   7	SIL	Bus "+" line	5 - Signal ground	Pulse generation	During transmission
   4	CG	Chassis ground	Body ground	Below 1 Ω	Always
   5	SG	Signal ground	Body ground	Below 1 Ω	Always
   16	BAT	Battery positive	Body ground	11 to 14 V	Always
   6	CANH	CAN bus line	CANL	54 to 69 Ω	IG switch OFF*
   6	CANH	HIGH-level CAN bus line	Battery positive	6 KΩ or higher	IG switch OFF*
   6	CANH	HIGH-level CAN bus line	CG	200 Ω or higher	IG switch OFF*
   14	CANL	LOW-level CAN bus line	Battery positive	6 KΩ or higher	IG switch OFF*
   14	CANL	LOW-level CAN bus line	CG	200 Ω or higher	IG switch OFF*

   NOTE:

   *: Before measuring the resistance, leave the vehicle as is for at least 1 minute and do not operate the ignition switch, any other switches or the doors.

Battery voltage

11 to 14 V

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

1. Check that the MIL illuminates when turning the ignition switch on (IG).

   If the MIL does not illuminate, there is a problem in the MIL circuit. Refer to MIL Circuit .

2. When the engine is started, the MIL should turn off.