Description & Operation
Multiplex control system is used for the body electrical system to provide a simplified wiring harness by using a communication bus which transfers signals between various Electronic Control Units (ECUs). See Fig 1. Body Electronics Area Network (BEAN) is used between body ECU, Engine Control Module (ECM), combination meter ECU, A/C amplifier and gateway ECU. See Fig 1. Combination meter ECU may also be referred to as meter ECU or combination meter, and A/C amplifier may also be referred to as air conditioning ECU. Audio Visual Communication Local Area Network (AVC-LAN) is used between the display ECU and audio components. See Fig 1. Serial data link has been provided between body ECU and door control receiver. In addition, a serial data link has been provided between ECM, Hybrid Vehicle (HV) ECU, brake ECU and battery ECU. See Fig 1. Multiplex control system uses the unidirectional communication called the Universal Asynchronous Receiver Transmitter (UART) between body ECU and power window master switch which contains the driver's door ECU. See Fig 1. Due to the data configuration difference between the BEAN and the AVC-LAN, the gateway ECU is used to convert the data between the BEAN and AVC-LAN to enable ECUs to exchange information over a single communication line.
Body ECU is provided with a function to communicate with a Toyota hand-held tester. Body ECU uses a self-diagnostic system in which Diagnostic Trouble Codes (DTC) are stored if a problem is detected in the communication bus. DTCs may be retrieved by using Toyota hand-held tester or using the open door indicator light. Body control ECU also contains a switch test function for related circuits. When system is in DTC retrieval mode, switches may be operated to determine condition of switch. If switch is operating properly, the relevant DTC will set while switch is being operated. If DTC is not set when switch is operated, an open circuit exists in the switch contacts. If DTC sets before switch is operated, switch is defective, as the switch contacts are stuck. Switch test function applies only to specified DTCs. For additional information, see RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.