2009+ Style STS Antenna Upgrade

Overall this is a fairly straight forward upgrade. Time to complete the upgrade will vary based on the technical skill of the individual.

When GM used the glass mount OnStar antenna, the new “Shark Fin” style was the version we see on the 2005-08 STS. Now the trend seems to be the 2009+ is called a “Shark Fin” antenna. The new style (as with the original 2005-08 version) is a quad-band antenna. It is capable of both analog and digital cellular communication along with a GPS antenna for the OnStar system and an S-Band antenna for XM radio. The OnStar GPS antenna is in no way connected to or utilized by the navigation radio. This system has a separate antenna located under the front dash. The OnStar GPS antenna allows for vehicle location when reported stolen, for assistance calls (emergency and crash notification) and Turn-By-Turn navigation (if equipped) with an active subscription.

Understanding the components…

The 2009+ style antenna base contains two of the three antennas. One is for OnStar GPS and the other is for S-Band (XM) radio. The colour matched fin that attaches to the base contains the OnStar voice communications antenna.

There are three coax cables (each of a different length) exiting through the bottom of the base assembly. The tan coloured coax is for the XM receiver, the black coax is for OnStar voice communications and the blue coax is for the OnStar GPS. These cables route toward the passenger side of the car.

There are several antenna base assemblies depending on the vehicle model. The CTS uses different connectors and is of no use in an STS. The Buick Lucerne uses a similar base, although I’m not certain what connectors it uses. I have been able to determine is the fin assembly is interchangeable between several vehicles. This can be very helpful and this will become apparent shortly.

My GM parts department shows a “paint to match” antenna fin (where matched colour antennas aren’t available). Unfortunately, this is less than desirable. The service manual cautions against this because paint can significantly decrease signal strength. The best solution is to purchase a colour matched antenna, of which GM offers several choices. In my case, “Sunset Blue” (Cadillac’s version of the colour) was discontinued after 2008 so there was no immediate option for me. Fortunately, in the Buick line, the Lucerne is offered for 2009 in “Transition Blue Metallic”. Both are paint code 78U. This became very helpful as I ordered the Lucerne antenna fin for my car and it’s a good match. If you want to upgrade but GM doesn’t offer your colour, check other lines with the same paint code and see if you can locate the correct part.

Necessary Tools, Parts and Supplies…

Depending on what you have available, various tools may be substituted but I used the following:

• 7mm Deep ¼” Socket
• 10mm Deep ¼” Socket
• 10mm Ratchet Style Box End Wrench
• #11 Surgical Scalpel
• Small Flat Metal File
• Roll of String
• General Purpose Masking Tape
• Non-marring Plastic Trim Panel Removal Tool
• Small Flat Blade Screwdriver
• Small Jeweller’s Screwdriver

The parts and supplies I used include:

• Foam Gasket Material – Adhesive on One Side
• 2009 Model Year STS Antenna Base (Shown Above) – P/N: 20815152
• 2009 Model Year Buick Lucerne Antenna Fin – P/N: 25840141 (Paint Code 400P or 78U)**
• Two Small Artist’s Paint Brushes
• Colour Matched Touch Up Paint
• Spray Can of Self-Etching Primer

** This part number will vary depending on your particular paint code. Check with your dealer to order the correct part number for your application.

The Procedure…

There are 7 basic steps to complete the upgrade. These include:

1. Preparing the antenna base assembly.
2. Lower the rear of the headliner to gain access to the antenna mounting bolt.
3. Removing the original antenna assembly.
4. Modifying the hole in the roof sheet metal.
5. Mounting the new antenna assembly.
6. Checking for water leaks.
7. Reassembling the vehicle.

Step One – Preparing the Antenna Base

The 2005-08 STS antenna requires two mounting holes. One is for the cables to pass through along with the cast section the retaining clip attaches to. The second hole is for a small pin to ensure that the antenna is installed facing the correct direction and that it can’t spin once installed. The primary mounting hole is ¾” round.

The 2009+ antenna only requires a single square mounting hole (with a keyed corner). The keying ensures the base can only be installed in one direction. If you position the point of the antenna base forward you’ll be fine with a completely square (3/4”) hole. You can see the shape of the hole GM uses on the template I created.

What you’ll find is the gasket material around the square hole on the new base is too small to cover the smaller hole that you will find on your roof. There are different thoughts on how to address this, one of which is to seal the hole with some silicone but I really dislike this approach. I acquired some new gasket material from a local industrial supply company. Using a calliper, steel ruler and surgical scalpel I manufactured a new gasket for the antenna base. This one extends further to ensure the small guide hole in the sheet metal will remain in the sealed area.

Link to Antenna Upgrade - Part II