Information Bus: Description and Operation

Multiplex Integrated Control System

How the Circuit Works

The Multiplex Control System sends digital signals between control units through shared wires to reduce the number of wires and reduce the weight of wire harnesses.

The input signals from each switch are converted to digital signals within the receiving control unit. The digital signals are sent from one control unit to another as serial data over dedicated communication lines. When the appropriate control unit receives the digital signal, it converts the signal back to an operational command, such as operating a relay. The multiplex control system schematic shows it's power, grounds, and communication lines. The ignition key light and ceiling light are shown because they are used to blink DTC's when the system is in the self-diagnostic mode.

There are two different networks within the multiplex system, they are:
- Body Controller Area Network (B-CAN)
- Fast Controller Area Network (F-CAN)

The fast controller area network (F-CAN) and body controller area network (B-CAN) share information between multiple electronic control units and work together to form the multiplex system.

B-CAN Network

B-CAN information is transmitted across the communication lines at a slower speed for convenience related systems that do not require the process speed of a fuel control system. The following control units operate on the B-CAN network:
- Gauge Control Module
- Relay Control Module
- Multiplex Integrated Control Unit (MICU)
- Door Multiplex Control Unit
- Combination Switch Control Unit
- Audio-HVAC Display Panel

The following systems are related to the B-CAN network:
- Gauges and Indicators
- Exterior lights
- Entry light control
- Interior lights
- Safety indicators
- Rear window defogger
- Horns (security and panic)
- Chimes (key, seatbelt and lights ON)
- Power windows
- Moonroof timer
- Wiper/washer
- Security
- Keyless entry
- Power door locks
- Climate control
- Key interlock
- Dash light brightness

F-CAN Network

F-CAN information is transmitted across the communication lines at a faster speed for "real time" functions such as fuel, emissions, and traction control data. The following control units operate on the F-CAN network:
- Gauge Control Module
- ECM/PCM
- Navigation Unit
- VSA Modulator-Control Unit

To allow both systems to share information, the gauge control module translates information from B-CAN to F-CAN and from F-CAN to B-CAN and operates on both networks.

Since messages on the F-CAN network are typically of higher importance, a second wire is used for communication circuit integrity monitoring.

For safety reasons, a backup circuit is also added to the headlight and wiper circuits of the B-CAN network in the event of a network wire, or ECU failure that would effect the system operation.