I recently bought a 2001 Chevy Blazer and it came with OnStar. I activated
it and OnStar was working great. I replaced my headunit with a Sony
aftermarket unit only to discover that OnStar needs the stock headunit. So,
I reinstalled the stock headunit and OnStar still does not work. It's as if
it is not getting any power. The buttons on the mirror do nothing and the
OnStar operator does not see the unit in their network. However, I triple
checked that I reconnected the headunit properly. I also can not find a
fuse that specifically is for the OnStar unit.

Any ideas???

Yep, OnStar does indeed need to go through your stock headunit for the
audio, or you can search eBay for an aftermarket adapter to allow
OnStar to play through an aftermarket head unit.

As for why your OnStar unit does not function anymore - that seems
unlikely to be related to your stereo replacement unless you or the
installer messed with some other wiring while installing the radio.
Even if your Blazer didn't HAVE a radio, and just had wires hanging
out of the dash, your OnStar unit would still be getting power and
functioning, you just wouldn't be able to hear it.

There are NOT many wires at all that link the OnStar unit with your
truck. Basically you have wires to the mirror buttons and microphone,
wires to the radio for audio, a ground wire, 12v power constant, 12v
ignition, and then data wires (UART for airbag, E&C bus for radio
control, and class 2 data for everything else) I don't know that there
is an inline fuse... I can dig up my schematics and check.

The OnStar VCU (cellular module) and VIU (vehicle interface/OnStar
brain) are mounted together on a metal bracket in the rear of your
Blazer on the right (passenger) side under the wheel well cover. Get
access to that and check all of your connections.

Contact me directly at holstdb @ comcast.net (remove spaces) if you
need further help.

Dave


"Earthlink" wrote in message k.net...
I recently bought a 2001 Chevy Blazer and it came with OnStar. I activated
it and OnStar was working great. I replaced my headunit with a Sony
aftermarket unit only to discover that OnStar needs the stock headunit. So,
I reinstalled the stock headunit and OnStar still does not work. It's as if
it is not getting any power. The buttons on the mirror do nothing and the
OnStar operator does not see the unit in their network. However, I triple
checked that I reconnected the headunit properly. I also can not find a
fuse that specifically is for the OnStar unit.

Any ideas???