Hello,

It'll somewhat depend on what transmission you will be using. I rather fancy using OS 12212156 or 12208322 and I'm presuming that you will be using the stock 1999, 512k byte, red / blue connector PCM common to that year.

But yes, you will be overwriting whatever OS is in your PCM now after you make a copy of it.

I completely recommend buying an additional PCM as a spare. And I also recommend making a bench harness out of junk yard parts powered by a decent, two amp power supply. The small 12 volt wall wart power supplies often konk out during the actual writing of the OS which can turn your PCM into a very nice door stop or wheel chock.

Rick