Description & Operation

WARNING: Vehicles are equipped with air bag supplemental restraint system. Before attempting repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in AIR BAG RESTRAINT SYSTEMS article.

Multiplex control system consists of the body control ECU, driver door ECU, passenger door ECU, theft-deterrent ECU and power seat ECU. They are all inter-linked by a communication bus that sends appropriate information back and forth to the pertinent ECU. The entire system has a self-diagnostic function, and Diagnostic Trouble Codes (DTCs) are stored by the body control ECU for diagnosis and retrieval. The OPEN DOOR indicator light is used to display DTCs, or scan tool can be connected to Data Link Connector 3 (DLC3) for diagnostic information retrieval.

Body control ECU also has switch and circuit test function for related circuits. When system is in DTC retrieval mode, switches can be operated to determine condition of switch and circuit. If circuit is operating properly, the relevant DTC will set while switch is being operated. If DTC does not set when switch is operated, an open circuit is present in either switch contacts or circuit. If DTC sets before switch is operated, switch is stuck or circuit is shorted. This function is relevant when testing for DTCs 21 through 24, and 41. See DIAGNOSTIC TESTS .