Multiplex Communication System Pre-Check

1. As shown in Fig 1, each ECU of this vehicle is connected by communication bus and it transmits each signal by communication. This communication bus is self-diagnosed by Body ECU and it memorizes DTC's when it detects communication stop to ECU or communication bus +B short or GND short. There is a possibility that Body ECU cannot self-diagnose accurately unless it doesn't work normal. So, please note that the troubleshooting of Body Electrical System should be done after confirming if Body ECU and Open door indicator works normal by 2. "BASIC INSPECTION" described later.
   Fig 1: Diagramming Communications Bus

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2. If DTC of ECU communication stop is output, there is a possibility of connector disconnection or 2 communication buses open. It will not become abnormal with only 1 communication bus open.
   Fig 2: Identifying Causes Of Communication Loss DTC's (1 Of 2)

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3. If 2 communication buses are open at the position as shown in the illustration, DTC of ECU communication stop between those 2 buses is output.
   Fig 3: Identifying Causes Of Communication Loss DTC's (2 Of 2)

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Inspection Body ECU 

1. Check Room Light Operation 
   NOTE: With this inspection body ECU CPU can be diagnosed if it works normal or not.

   CHECK: 

   Check if the room light works normal at DOOR position.

   NOTE: If the room light illuminates normally, the DTC can be output without using the diagnosis check wire by the way as described in step .
   1. OK:  Go to step  1 of INSPECT OPEN DOOR INDICATOR LIGHT.
   2. NG:  Go to step  2.
2. Check Interior Light System (Except Body ECU), See INTERIOR LIGHT SYSTEM
   1. OK:  Replace the body ECU.
   2. NG:  Repair of replace malfunction part.

INSPECT OPEN DOOR INDICATOR LIGHT

1. Check Open Door Indicator Light 
   Fig 4: Locating Open Door Indicator Light

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002