Diagnosis System

1. The ECU uses ISO 15765-4 for communication. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 15765-4 format.
   Fig 1: Identifying DLC3 Connector Terminal Identification

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   Symbols (Terminal No.)	Terminal Description	Condition	Specified condition
   SIL (7) - SG (5)	Bus "+" line	During transmission	Pulse generation
   CG (4) - Body ground	Chassis ground	Always	Below 1 Ω
   SG (5) - Body ground	Signal ground	Always	Below 1 Ω
   BAT (16) - Body ground	Battery positive	Always	11 to 14 V

   HINT: 

   If the display shows UNABLE TO CONNECT TO VEHICLE when connecting the cable of the Techstream to the DLC3, turning the ignition switch on (IG) and operating the Techstream, there is a problem on the vehicle side or tool side.

   • If communication is normal when the tool is connected to another vehicle, inspect the DLC3 on the original vehicle.
   • If communication is still not possible when the tool is connected to another vehicle, the problem is probably in the tool itself. Consult the Service Department listed in the tool's instruction manual.

HINT: 

The most difficult case in troubleshooting is when no symptoms occur. In such cases, a thorough customer problem analysis must be carried out. Then the same or similar conditions and environment in which the problem occurred in the customer's vehicle should be simulated. No matter how experienced or skilled a technician may be, if he proceeds to troubleshoot without confirming the problem symptoms, he will likely overlook something important and make a wrong guess at some points in the repair operation.

This leads to a standstill in troubleshooting.

1. Vibration method: When vibration seems to be the major cause.
   Fig 2: Identifying Vibrating Connectors

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   HINT: 

   Perform the simulation method only during the primary check period (for approximately 6 seconds after the ignition switch is turned on (IG)).

   1. Slightly vibrate the part of the sensor considered to be the problem cause with your fingers and check whether the malfunction occurs.

      HINT: 

      Shaking the relays too strongly may result in open relays.

   2. Slightly shake the connector vertically and horizontally.
   3. Slightly shake the wire harness vertically and horizontally.

      The connector joint and fulcrum of the vibration are the major areas to be checked thoroughly.

2. Simulation method for DTC B1794: Turn the ignition switch from the off to on (IG), hold for 10 seconds, and back to off again 50 times in a row.

   HINT: 

   DTC B1794 is output if the occupant classification ECU receives the ignition switch off-on (IG)-off signal 50 times in a row when a malfunction occurs in the power circuit for the occupant classification system.

1. Initial check.
   1. Turn the ignition switch on (IG).
   2. The passenger airbag ON/OFF indicator ("ON" and "OFF") come on for approximately 4 seconds, then goes off for approximately 2 seconds.
   3. Approximately 6 seconds after the ignition switch is turned to on (IG), the passenger airbag ON/OFF indicator will be ON/OFF depending on the conditions listed below.

      Front Passenger Seat Condition	Passenger Airbag ON/OFF Indicator		SRS Warning Light
      	ON Indicator	OFF Indicator
      Vacant	OFF	OFF	OFF
      Adult is seated.	ON	OFF	OFF
      Child is seated.	OFF	ON	OFF
      Child restraint system is set.	OFF	ON	OFF
      Front passenger occupant classification system failure	OFF	ON	ON

      HINT: 

      • The passenger airbag ON/OFF indicator is based on the timing chart below in order to check the indicator light circuit.
        Fig 3: Identifying Timing Chart Diagram

        Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      • When the occupant classification system has trouble, both the SRS warning light and the passenger airbag ON/OFF indicator ("OFF") come on. In this case, check the DTCs in the "AIRBAG SYSTEM" first.

1. Turn the ignition switch on (IG).
   Fig 4: Identifying Passenger Airbag ON/OFF Indicator

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Check that the passenger airbag ON/OFF indicator ("ON" and "OFF") come on for approximately 4 seconds, then goes off for approximately 2 seconds.

   HINT: 

   Refer to the table in step 3 regarding the passenger airbag ON/OFF indicator when the ignition switch is turned to on (IG) and approximately 6 seconds pass.