From an earlier post, you said the shop person said the 'Fluid was like coke'. Was he refering to the radiator or the tranny? If he said the ATF was black, then the tranny is toast.

Because you can drive normally in D, but not in R, I suspect that the bands inside the tranny are shot for R. Winter weather is hard on automatics when the ATF is cold, having low levels of ATF make things worse and create more wear. And true internal failure usually starts with Reverse. Also, failure of Reverse gear, by itself, will not generate a code.

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My back feels better when I sit in a Volvo seat