Thank you for the mention in your post. I found an article relating to HES failures on R1100's and the symptoms were remarkably similar to yours. Seems the wiring suffers from the heat the most. I believe the author insulated the wires from the sensor to the connection which increased the life of the HES unit substantially. If you saved your old plate, there are replacement sensors available for under $30 apiece. Drill out the rivets and bolt on new sensors, insulate the wires and you've got a spare.
Yes sir - it may well be that my bench test didn't pick up the fault because it was the wires that were fried rather than the sensors. Either that or it was a *heat* issue rather than a *temperature* issue which is what Lee describes....and any engineer worth his salt will appreciate the difference between heat and temperature.
Either way - the HES wear out on BMW motorcycles - not just the K-bikes. That's no secret - and the symptoms are pretty obvious (more so now that this thread exists I hope).
I also followed the threads where people bought replacement sensors for a few dollars and rebuilt their own sensor plates. I was all prepared to do that but unfortunately Honeywell no longer sells the sensors - part number 2AV54. They were discontinued in 2008 or something like that.
There are Chinese sensors available, but they are $60 each and so far as I can tell no-one has documented a rebuild using them yet. I considered being that guy - but at a cost of $120, a whole lot of work, and a finite risk of failure - I just coughed up the $400 for the factory part instead. I'm glad I did.
Cheers guys - here's hoping that's all the technical trouble I have for a while. I put another 300 miles on the bike today - what a joy to ride this thing is. :clap