Pull copies of your credit reports from either
www.annualcreditreport.com or through the three bureaus directly (Trans Union, Experian or Equifax).
Look in the "Public Records" section for the judgement. If it is there, contact the court it was through and find out what it was supposedly for.
It is possible that you were a victim of a mixed file at the auto dealership. Since the bureaus do not use exact match criteria (only 7 of 9 digits in your social security number, two letters of first name and ZERO of last name), it's possible you have someone else's info.
If so, contact the bureaus to dispute it.
LG