2003 Cummins engine sensor identification

This gOOgle search...

turbo boost sensor ISB Freightliner

...produced a number of hits, with Big Machine Parts being one of the more interesting. The pictured one resembles the "nut" part of yours, and maybe the broken plastic piece still in its connector. But it refers to a later model 6.7 ISB. Still, they had an "Ask Us" feature that could help you, maybe even with that fan.

The search also turned up other sources, even Amazon, and some pictures (which I usually find very untrustworthy) and links to RV.net and other forums.

Ah well that sucks. Why is it the part always costs more!

No Scott, it is shaped like a nut. I wish it was that one. The Freightliner dealer thought it was the Intake pressure senor and it was $110. I curse my size 14 shoes!!

Is it the item shown in the video?
Does it look like this: sensor

Got link to work. Sorry Scott that sensor is for a Dodge Cummins, Mine is in a Freightliner rear pusher RV. Thanks anyway!

I'm trying to post a picture, no luck yet.

If it's a plastic sensor with a connector pointing straight up and is held in by two screws, it's your MAP sensor (boost sensor).
See this video: Linkaroonie
If it's the sensor that had a threaded body and is in the the fuel rail, that's your rail pressure sensor.
(BTW, it's a "Cummins")