If BOTH seats fail at the EXACT SAME TIME, the seat relay under the dash, driver's side, is bad. A skilled technician can resolder the cracked diodes or you can buy a new relay for around $25 and plug it in yourself.

If it is one seat that does it, it can be a bad switch, bad limit sensor, etc. - that gets more complicated. But if BOTH seats fail at the VERY SAME TIME, its the seat relay. Very common.