It's possible, either way, nothing to worry about. Did you give consent or not? If not, fight that shit. Tell your lawyer/defender you want to file a motion to supress all evidence. It's worked for me before. If you DID give consent, and they charge you, just take the charge man, it's just a crappy misdemeanor charge that you're going to get slapped on the wrist for.

The reason they told you you might be getting a subpoena in the mail is because they have to turn the case over to the DA and see if they want to prosecute. Chances are, they won't, but that's not guaranteed.

Either way may, just chalk it up to a learning experience and be smarter next time.

Did the pig tell you why he stopped you in the first place? and do you remember if you actually gave consent? Feel free to contact me on AIM I know a lot about this shiet.