Body Electrical Control Module
The Body Electrical Control Module (BECM) is located below the front passenger seat and is secured to the floor pan with two nuts and a screw.
The BECM controls, monitors and provides power supplies to many of the vehicle electrical functions. The BECM interfaces with other Electronic Control Units (ECU's) via hardwired connections or via a digital serial data bus as follows:
- Supplemental Restraint System Diagnostic Control Unit (SRS DCU)
- Anti-Lock Braking Electronic Control Unit (ABS ECU)
- Heating, Ventilation & Air Conditioning Electronic Control Unit (HEVAC ECU)
- Cruise Control ECU
- Engine Control Module
- Electronic Air Suspension Electronic Control Unit (EAS ECU)
- Transfer Box ECU
- Electronic Automatic Transmission Electronic Control Unit (EAT ECU)
- Instrument Pack
The BECM also communicates with several outstations via a digital serial data bus. The data bus allows the BECM to "talk" to the outstations by passing electrical information through the same wires. Each data bus comprises five wires as follows:
- Feed Wire - Battery Voltage Supply
- Earth Wire - Vehicle Earth
- Clock Wire - Reference Signal
- Signal Wire - Transmits Digital Signals
- Direction Wire - Identifies Direction Of Signal
The data bus reduces the number of wires required to perform the various electrical functions. Each wire in the data bus is duplicated to increase the reliability of the connections.
The BECM has two modes of operation; activation mode or sleep mode. A number of inputs to the BECM will change the state of the BECM from sleep to activation mode. Sleep mode is required to avoid excessive drain on the vehicle battery when the vehicle is not being used.
Sleep mode is entered when certain timers have "timed out" (i.e. courtesy lights go off) and all activation inputs have been inactive for more than two minutes. If the vehicle is unlocked in sleep mode, the current used by the BECM is 30 mA. If the vehicle alarm is armed in sleep mode, the current used by the BECM increases to 40 mA.
When an activation input is sensed and the BECM "wakes up", the current used by the BECM increases to approximately 1 Amp.
The BECM is connected to the other ECU's and the electrical functions it controls by nineteen connectors. Tables containing a description of the connector pins and the functions they serve are detailed later in this section. See CONNECTOR IDENTIFICATION .