Description & Operation
The multiplex control system consists of a body Electronic Control Unit (ECU) connected to 2 communication buses. The door system communication bus has driver's door ECU, passenger's front door ECU, driver's rear door ECU, passenger's rear door ECU, seat ECU (if equipped), sun roof ECU (if equipped) and tilt and telescopic ECU. The instrument panel system bus has instrument cluster ECU, A/C ECU, multi-display ECU and ECM. See Fig 1. Both buses are connected to body ECU through their own bus cut-relay. The multiplex control system is also equipped with a self-diagnostic function. Some electrical systems are directly connected to the body ECU, while some electrical loads and switches are connected to the appropriate ECU.
Vehicle body electrical systems are controlled by serial communication in which each ECU is linked together by a single communication line. Once signals are received from door lock control switch or door courtesy light switch, each ECU determines the condition of the switches and doors. Each ECU converts the signal to digital signals and then outputs them to other ECUs. The body ECU receives these digital signals then determines the conditions of the switches and doors to use various controls to operate a specific system or motor. However, if there are no changes in input signals because doors are still closed or switches are not used within 30 seconds, the body ECU interrupts the communication to save battery power. After interruption, any changes in input signals will cause communication to resume.