Diagnosis System

The occupant classification ECU controls the functions of the occupant classification system on the vehicle. Data of the occupant classification system can be read through the Data Link Connector 3 (DLC3) of the vehicle. When the system seems to be malfunctioning, use the Techstream to check for a malfunction and perform repairs.

Fig 1: Identifying DLC3 Connector Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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.

• 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 to 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 on the original vehicle.
• If communication is still not possible when the tool is connected to another vehicle, the problem is probably in the tester itself. Consult the Service Department listed in the tester'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. A simulation of the same or similar conditions and environment in which the problem occurred in the customer's vehicle should be carried out. No matter how much skill or experience a technician has, troubleshooting without confirming the problem symptoms will lead to important repairs being overlooked and mistakes or delays.

1. Vibration method:

   When vibration seems to be the major cause.

   Fig 2: Symptom Simulation - Vibration Method

   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 to ON).

   1. Slightly vibrate the part of the sensor considered to be the cause of the problem 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 B1795:

   Turn the ignition switch from off to ON, hold the position for 10 seconds, and then turn it back to the off position again 50 times in a row.

   HINT: 

   DTC B1795 is output if the occupant classification ECU receives the ignition switch off - ON - 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 to ON.
   2. The passenger airbag ON/OFF indicator (ON and OFF) comes on for approximately 4 seconds, then goes off for approximately 2 seconds.
   3. Approximately 6 seconds after the ignition switch is turned to ON, the passenger airbag ON/OFF indicator will be ON/OFF depending on the conditions listed below.

      Condition	ON Indicator	OFF Indicator
      Vacant	OFF	OFF
      Adult is seated	ON	OFF
      Child is seated	OFF	ON
      Child restraint system is set	OFF	ON
      Front passenger occupant classification system failure	OFF	ON

      HINT: 

      • The passenger airbag ON/OFF indicator operates based on the timing chart below in order to check the indicator light circuit.
        Fig 3: Passenger Airbag ON/OFF Indicator Timing Chart

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

1. Turn the ignition switch to ON.
   Fig 4: Identifying Passenger Airbag ON/OFF Indicator Light

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Check that the passenger airbag ON/OFF indicators come on for approximately 4 seconds, then go off for approximately 2 seconds.

   HINT: 

   Refer to the table in the previous step regarding the passenger airbag ON/OFF indicator when approximately 6 seconds have elapsed after the ignition switch is turned to ON.