I wish that error code could be more specific.
Could be a valve body issue- which would line up well with the "tranny is in decline" thesis. The fluid check for quality and level will settle that issue. The volume of the fluid varies with temperature, and perhaps cold weather put it below a threshhold for the torque converter? I'm fishing. Ya gotta look and see.
I tend to agree with Ryan that the lack of onset symptoms makes it seem electrical. Hopefully it's just one of those speed sensors in the valve body, as it's pretty cheap.
Could be a module failure. I had that on my 95 540i. I was getting tranny codes for temp, sensors, and solenoids. Opened it expecting to see burnt fluid etc, yet it was clean. Did the Kirt K valve body swap, preventatively, and even with a brand new harness on it I was pulling codes and in trans prog hell. Kirt sent me a known good egs module, and presto! fixed. I recently had an abs module go on an e39- it lit up the dash warnings like a christmas tree: ABS Brake DSC CE- after testing all the speed sensors, I determined it was the module, and sent it to "Module Master" for a rebuild, and it's as good as new now.
anyway,
Before spending bux, it's worth seeing if you can borrow a known good one for a minute. From my experience it's cheaper to eliminate that possibility first.
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