If you have a light use car, you might solve the problem by simply running teh shift lever back and forth a bunch of times (engine off). that is also referenced in Bay 13. Apparently one cause of the warning lights and intermittent failure to operate correctly is just corrosion that builds up on teh switch contacts. My '95 855T had the flashing up arrow and check engine light, and sometimes the transmission would go into winter mode on its own. So far all of this has been completely cured by the above - running shifter up and down a coule of dozen times. Its 2 months now, and so far all is well.
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Mike Sullivan ('91 745 (171k), '93 965 (147k), '95 855T (60k), '98 V70XC (78k). Past Volvo's: '85 744 (256k), '86 245 (165k), '86 245 (195k), '88 745 (208k).