What's this fuel gauge for?

[karlcchen]

I was trying to replace my 2004 R1150RT fuel filter. I accidentally break the plastic (fuel gauge) when pulling the float for fuel gauge out. I simply removed it and expect to see no fuel bars display. But display continue to work fine!

The sender I talked about is similar to picture in this thread, with reostat contacts:
http://www.bmwmoa.org/forum/showthread.php?t=28080

It turn out there is another fuel gauge in the fuel tank that control the fuel capacity display bars. So what's this fuel gauge by the fuel pump for?
Service manual says this gauge is an option on some models. On the above thread, everyone is talking about cleaning it to have accurate display, but removed it continue to have perfect display!

Thanks,
Karl

[ArthurKnowles]

If I recall correctly the RT line has two sensors. One for the RID and one for the warning light (you are on empty, so now's a good time to put gas in it or suffeer the consequenses light) on the dash. I suspect this is the latter one have damaged if the RID is still working.

[Frankjv]

Karl,
Arthur is right. There are two fuel gauges on the RT. The gauge attached to the access plate on the gas tank is the low fuel indicator light. The fuel gauge that’s connected to the RID is in a tube that is attached to the top of the fuel tank. When you removed the access plate on the fuel tank there is a two wire connector that you unplugged to remove the plate. That connector is attached to the RID fuel gauge.

Hope this helps.

Frank
04 1150RT

[karlcchen]

So it is for warning light. But when I see its rheostat, it has as many fine gradation as there are bars in display which means it can tell fuel capacity, not just low fuel.

Do they use the second fuel gauge to cross-verify primary fuel gauge's accuracy?

Karl

[Frankjv]

It seemed pretty strange to me too. I don't think there is any connection between the two. My problem ended up being a broken ground wire in the harness where it passes through a plastic plug in the access plate.

Check out these threads from bmwsporttouring.com. They also illustrate the confusion between the two gauges:

http://bmwsporttouring.com/ubbthreads/ubbthreads.php?ubb=showflat&Board=1&Number=151612&Searchpage=2&Main=15559&Words=fuel+gage&topic=0&Search=true#Post151612

http://bmwsporttouring.com/ubbthreads/ubbthreads.php?ubb=showflat&Board=1&Number=286276&Searchpage=1&Main=26781&Words=gas+gage&topic=0&Search=true#Post286276

By the way, one of these threads referenced pin positions on the external connector that I found to be incorrect. I might still have the correct pinouts for an 04 RT if you need them.

Hope this helps,
Frank