SAN JOSE (AP) — Authorities say a Tesla driver, who said he thought his car was in Autopilot mode, crashed into the back of a firetruck in San Jose.

The California Highway Patrol says the Tesla rear-ended a fire engine that was stopped with its emergency lights activated along US-101 around 1 a.m. Saturday.

The 37-year-old driver, Michael Tran, told officers, “I think I had auto-pilot on.”

Tran was later arrested on suspicion of drunken driving. It wasn’t immediately clear if he had an attorney.

Tesla’s semi-autonomous Autopilot mode has come under scrutiny following other recent crashes. The carmaker says the function is not designed to avoid a collision and warns drivers not to rely on it entirely.

It was unclear whether Autopilot was activated. Tesla says in a statement that it “has not yet received any data from the car, but we are working to establish the facts of the incident.”