As i previously owned a SAAB there was much disscusion on the SAAB board about this and I have taken apart a few modern SAAB seats, which are made by Brose( so are your M3 seats). The heating elements are broke into 2 parts, upper and lower.The lower element useually gets broken due to a sharp blunt object being put on the seat. For example, the full force of a knee or a heavy dogs paw. This break can be repaired if you take the seat apart. Your can isolate the issue with a ohm meter. The 2 parts of the seat are hooked together in series. So there should be a 2 prong plug that you can pull apart between the seats to check each half. If it is in fact the bottom it will be much easier to disassemble. A small burn mark will show the break, which can be soldered and heat shrinked. or you can probley buy the whole lower foam w/the heater attached(you could for a SAAB). You may also need a set of hog ring plyers and a auto upostery book. If you read up a little this should only take you a afternoon. )