Today, I just received a Bachmann Union Pacific® #1148 (Dependable Transportation)-ALCO S2-DCC(HO) that I had ordered from ModelTrainStuff.com. Initially, the unit would not run on the default DCC #3, and judging from the condition of the box and the absence of an instruction sheet, I’m guessing that this unit was previously purchased and returned. Anyhow, after some headscratching and a few prayers, I stumbled upon my layout’s DCC instruction book from Bachmann, and there were directions on how to reprogram a unit that had been assigned a number higher than 10 (that’s the highest number on the Bachmann DCC controller). So, I reprogrammed it, per the instructions, and voila, it ran, and had sound. I must say that the acceleration and decelleration sound quality is really quite good. Both short and long horn sounds get pretty much drowned-out by the prime mover, but if having to make a choice, I’ll take the diesel’s sounds. Anyhow, the Bachmann advertisements reference 3 horns for this unit. Since I only have 2, I was wondering if anyone could recommend how I can uncover/retrieve the 3rd horn sound. Thanks all!
Update to my post from this weekend: I made the tough decision to send this unit back to the store. I say “tough” because that was the last unit in stock for the particular road name I was wanting. Oh well, I ordered a Bachmann Erie and Lackawana S4 as a replacement…looking forward to a new unit performing better than a store return 
Steve
I have two of the Santa Fe Zebra Stripe Alco S-4 Sound Value locos and they are indeed rather SWEEEEEET running models. According to the Bachmann instruction sheet I downloaded from the Soundtraxx website, you need to access CV #115 to select one of the three horn sounds. The default value (0) results in a Wabco E2 horn. Changing CV #115 to a value of 1 results in a Leslie A125/A200 Combo horn sound. A value of 2 results in a Nathan P3 horn. I would assume the S-2 settings/horn options are similar. If your Bachmann DCC controller will not allow you to acces CV #115, someone in your area with a more advanced DCC system might be able to help you.
Bachmann web site and SoundTraxx have CV list.
Bachamnn site has forums and company reps. Lots of good data for Bachmann products. Repair and parts info.
Reset a decoder is the first thing to do with any issues.
CV8, enter 8, cycle track power and headlight should flash sixteen times for a successful reset.
Rich