The tire pressure light on our Toyota started coming on every time we drive. Each time I'd manually check the tires, and they'd all be identically and fully inflated. Got it into the shop today, and turns out they have battery powered sensors inside the tire, and one's battery had died (while the other 3 are on the verge). Cost to fix: about $500 including parts and labor.
Mechanic: Is the light driving you nuts?
Me: Y'all got some duck tape?
Mechanic: *tears off a piece and hands it to me*