I've seen the ZGM on a 745i fail for (presumably) no good reason, car wouldn't get out of limp mode until unit was replaced (has to be new, 850$) and coded (an hour labour).
Hot: 2001 Estoril M Roadster
ZCP 19's, ZHP knob, JL 8W3
Cold: 2002 TiAg M3 6mt
ZCP 19's supersports, ZHP knob, UUC short shift GROM, OEM 18's w310's,
http://absolutehid.ca hid kit