LOS ANGELES — The “check engine” light of the BMW had been glowing for a few days when its owner pulled up to the valet drop-off at Ink, the much-discussed restaurant opened here two years ago by Michael Voltaggio, a “Top Chef” reality show winner.

The driver was greeted for her lunch first by Bruno Cavallini, 32, whose expertise with cars goes far deeper than what is required by his job with the valet parking company at Ink. When Mr. Cavallini asked how she liked the BMW — something he almost always does with customers who drive performance cars — she mentioned the warning light.

Mr. Cavallini dug out a hand-held computer code reader from the trunk of his 2004 BMW M3 and plugged it into the diagnostic port of woman’s car before driving around to the restaurant’s rear lot.

When she returned after lunch, Mr. Cavallini explained the problem: her BMW had a bad coolant sensor, and it should cost about $90, not including labor, to fix.