I have a 2003 M5 with MKIV NAV. Works fine most of the time. Locks up, but buttons work. ie radio stations, scan search etc. Just no display. When it does lock up, the unitl will perform a reset after about 5-10minuets of being locked.

At times, when locking up, the map screen may update occasionally. When this happens the general travel direction is correct, but it shows me somewhere parallel to my current route. Acts like it is not correctly interpreting the satellites.

More troubleshooting revealed that this situation always happens when the surface of the car gets hot from the sun. Everything is fine in the morning when i pull out of the garage. And if it is a cold, overcast day, like in December, i never have a problem. I noticed that the NAV unit is extremely hot on a sunny day. the black surface of the car, and the NAV's mounting bracket in the trunk, are very, very hot. I suspected a problem with the NAV/DVD unit in the trunk. Until, one cold, but very sunny, day (if florida), the NAV/Map locked up. I ran back to the trunk, touched the NAV unit, and it was stone cold!!???

now i suspect the antenna. The dealer said they get a "receiver error". however because of what looks like water marks on the NAV unit, they refuse to repair it under warranty. I don't think it is the NAV unit.

Any thoughts?