He debuted at the 1999 NAPA Auto Parts 200 at California Speedway with the #68 Hot Wheels Dodge. Contreras would drive the car to a 14th place finish in his first race. In 2000, he competed in the full season for Impact Motorsports in #12 Hot Wheels Dodge. He has two top tens during the season and finished 17th in points. He moved to Petty Enterprises in 2001 along with his sponsor Hot Wheels. He would again post two top tens on the season and move up to 14th in the overall points standings. For the 2002 season, Contreras returned with to the series with Petty Enterprises and again turned in another solid season. He would post one top ten on the season and would rank 16th in the overall point standings. He made his return to the Truck Series in 2010 after it was renamed the Camping World Truck Series, driving the #00 Chevy for the 2010 NextEra Energy Resources 250 for the first time since 2002, finishing 14th.
In 2014, Contreras returned to the Nationwide Series, competing in a limited number of races for Rick Ware Racing.