Restraints and Safety Systems: Description and Operation

High Speed Controller Area Network (HS-CAN)
This vehicle utilizes a communication system called a high-speed controller area network (HS-CAN). The HS-CAN consists of a twisted pair of wires connected to the following:
- Anti-lock brake system (ABS) module
- Instrument cluster module
- Powertrain control module (PCM)
- Transmission control module (TCM)
- Four wheel drive (4WD) control module (if equipped)
- Restraints control module (RCM)
- Air suspension (vehicle dynamics) module (VDM) (if equipped)
- Data link connector (DLC)

The HS-CAN circuits use a bias voltage of approximately 2.5 volts, one is a positive 2.5 volts while the other is a negative 2.5 volts. The HS-CAN also uses 2 terminating resistors, one contained within the PCM, the other in the instrument cluster module. The terminating resistors are not serviced separately. The terminating resistors have a value of 120 ohms each, for a normal operating system total of 60 ohms. The HS-CAN will operate with only one terminating resistor and has the capability to communicate some messages to some of the control modules with only one circuit functioning, but at a reduced rate of performance.

Electrical System
The electrical system that supports the air bag SRS:
- is powered from the battery through the ignition circuit.
- provides the electrical path from the restraints control module (RCM) to the SRS components.
- provides the electrical path from the RCM to the air bag warning indicator.
- provides the electrical path from the RCM to the data link connector (DLC).
- provides the electrical path from the RCM to the instrument cluster module.

LOOPS/SQUIB
All deployable devices contain an initiating device called a squib. The squib is part of the deployment loop. Air bag/safety canopy modules can contain more than one squib, some vehicles may have up to 4 squibs in one air bag module. Squibs are often referred to as loops during the diagnostic process.

SECONDARY AIR BAG WARNING (CHIME)
The secondary air bag warning chime, is an audible chime controlled by the instrument cluster module (ICM). If the ICM has detected a fault with the air bag warning indicator a diagnostic trouble code (DTC) will be stored in memory of the ICM. Upon receiving the message from the restraints control module (RCM) that a SRS fault has been detected, the ICM will sound the secondary air bag warning chime in a pattern of 5 sets of 5 beeps.