Subaru Forester 2.5X 2003 Technicians Reference Booklet page 24

2003 New Model Update
The VCU and VIU are installed above and below
the radio. These parts as well as the remaining
OnStar components are installed at SIA. Upon
installation the codes for VCU and VIU are
recorded and reported to OnStar. This process
makes interchanging parts from vehicle to vehicle
impossible. Parts replacement of the VCU and
or VIU requires a phone call to OnStar to report
the new code numbers.
The 3 Button Module provides the input from the
driver to make a cellular call, receive a cellular
call and end a cellular call. The 3 Button Module
is also equipped with a 2 color led that indicates
trouble with the OnStar system. Green
illumination indicates a present problem while
red illumination indicates a past problem during
diagnostic mode. During normal operation the
green LED indicates no problem and OnStar is
ready for operation.
The VCU is the cell phone unit of the vehicle. It
is connected to the combined cellular / GPS
antenna and the VIU.
The VIU receives input signals and provides out
put signals to perform cellular phone service and
vehicle assistance.
The Radio receives output signals from the VIU.
The VIU will turn the Radio on, if it is off, bypass
the normal sound system for speaker use and
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turn the Radio off, if it was off before the output
signal from the VIU was generated. Three wires
are used to control and communicate with the
Radio, two wires for the voice output and one
wire for the bypass control.
The Security control module receives 2 input
signals from the VIU, arm and disarm. Both
signals are sent to the security control module
on the same wire. The difference between the
two signals is amount of time the wire stays
grounded. The arm signal provides 20
milliseconds of ground time while the disarm
signal provides 80 milliseconds of ground time.
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(912) Legacy
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June 2002