Gs 400

[cheath]

Does anyone know why the drivers seat heater won't heat?

[1990LS400]

The failure of a seat heater is often caused by a broken wire in the seat heater grid. A seat heater works much like an electric blanket.

There is a long (11 page) diagnostic procedure in my repair manual for my 00 LS for the seat heaters -- too long to scan and post here and it might be a little different for your GS. The diagnostic procedure is mostly checking continuity and resistance. If you don't have access to a repair manual, the procedure can be downloaded from Lexus Techinfo.