[TeeCee]

The two elements are in series, so it's a "one gone, both gone" thing.
Get underneath the seat and disconnect the heating connector. Test for continuity through the seat. If nothing here then one has gone. Hunt around and you'll find the connection where the seat back heater plugs to the base one. Pull this and test for continuity on the back. If nothing, it's gone. If ok, the base has gone.

I have replaced both, neither is a difficult job. Just be careful peeling off the old element and use cable ties on reassembly to replace the hog rings holding the cover centre section in place. Plenty of pics and "how to's" if you look around here.