2004 Avalanche - factory XM antenna?

[bobkat]

I just picked up a real nice '04 Avalanche that has a little antenna on the roof on the driver's side. This truck has the UC6 factory head unit and UQ7 Bose speaker system. It does not have factory XM and I want to add some portable unit. My question is:

Is this little antenna for Onstar only or XM as well?

If for XM would there be a vacant connector somewhere behind the glove box? I dropped the glove box door and had a quick look around - there is no XM module (of course) nor can I see an antenna connector anywhere hanging down ready to be hooked up.

Where is the actual Onstar module? There is some silver box above the glove box area with a wire harness and some strange looking foam covered tube going to it. Airbag module?

I'm lost...

Thanks for all replies.

[I CHNGE]

In '04 the OnStar antenna was mounted on the driver side roof and had a small black shaft screwed to the base...for factory XM...a shark fin type antenna was mounted in the same location but on the passenger side roof.

The '04 Onstar module is located about 1 inch below the top dash cover panel.....about 3 inches in from where the windshield "bottoms out" and just slightly to the right of the dash mounted light sensor for your headlights.  To access the OnStar module requires removing the top dash pad cover panel and removing an internal cross brace...then it is easliy removed/replaced/whatever...

[bobkat]

Thanks for that info.

Looks like I'll be mounting an external XM antenna somewhere... not keen on having exposed cabling so I must check out potential locations carefully.

I don't need to get at the Onstar module - I only wondered if that silver box was Onstar - but having looked at it again I think it must be part of the HVAC system. That would explain the little steel tubing attached to it.