The shifter cable has stuck on my cargo bike. It has a shimano nexus 8 internal gear hub, with a full cable housing from the shifter to the hub. The cable housing says "shimano sealed", presumably to prevent problems like this. The shifter is stuck in 4th gear - which is lucky, since if I had to pick a single gear that would be the one I'd pick, and I usually leave it in 3rd gear.
When I shift down to 1 or 2, I get lots (maybe 1/2") of slack at the shifter end and can easily inspect the cable housing end (neat - it's "sealed"). At the hub, I can detension the cable by pushing counterclockwise on the hub and can similarly get lots of slack. Since the shifter and hub can both move, I'm deducing that the cable must be stuck somewhere inside the housing.
If it was regular housing, the typical advice seems to be to flush the housing with WD-40 to get the water out, and then lubricate with light oil. What should I do with this "sealed" housing? The weather is supposed to warm up in a couple of days, so I expect it to improve at least temporarily, but it's only a matter of time before the mercury drops below freezing and stays there until sometime in March.
In hindsight, this isn't such a surprise. I leave the bike outside, covered by a tarp, and the tarp rests on the right handlebar and after a heavy rain the handlebars are quite wet. Yesterday we had lots of rain that then turned to ice pellets and snow. I don't have time to build a bike shed, so I'm planning to cover the handlebars with heavy plastic bags to try to prevent this from happening again. If you have other suggestions, please share!