What was the title of Pixar’s first Cars short film?

Pixar’s first Cars short film was titled Mater and the Ghostlight.

Mater and the Ghostlight was released in 2006 and features Mater being frightened by a mysterious blue light after his friends play a prank on him. The short expands the world of Radiator Springs while focusing on Mater’s comic personality rather than on a major race.

It was distributed with Cars home-video releases and became one of the earliest pieces of Cars material outside the feature film. The ghostlight is a folklore-inspired roadside light that gives the short its central visual gag.

Later Cars shorts included the Cars Toons series, such as Rescue Squad Mater and Tokyo Mater, as well as The Radiator Springs 500½. Those titles are sometimes confused with Mater and the Ghostlight, but they were released later and are separate shorts.