Lexus ES cruise control malfunction

I had a similar problem with my ES. Check the pedal switch; sometimes they get wonky. It might be worth looking into the clock spring too, though that usually affects more than just the cruise control. The dashboard light should come on, though, if it's the clock spring. Does it?

Thanks! Is the pedal switch something I can easily check myself, or should I take it to a professional? And how would I know if it's the clock spring for sure?

Checking the pedal switch is doable, but you'll need to get under the dash, which can be a pain. As for the clock spring, if other things like your horn or steering wheel controls are acting up, that's a sign. Otherwise, best get it checked by a workshop to be sure. Sounds like the connection is defective.

Took it to the shop, and it turns out a cable connection was defective, like you suggested. Repair cost me 95€.