The contacts in the rotary switch become oxidized over time, the computer "thinks" the switch has become disconnected.

The "correct" (dealer, warranty) solution is replace the switch. The "cheap, easy" temporary solution is to quickly run the switch through all it's positions a few times, this usually removes enough oxidation from the contacts and the switch will be OK again for a while. I last replaced my switch a couple of years ago, I would have chosen the "cheap, easy" solution instead since lately the switch has been acting up again since the temperatures have dropped.

-BTC

'98 V70 T5M, 152k mi, front IPD stabilizer bar, rear factory HD bar, Bilstein HD, Volvo strut tower brace and skidplate, e-codes, V-1, Mobil-1 since new