2002 Volvo V70 Intermittently Won't Shift Out of Low

[alleycat44]

My 2002 Volvo V70 XC AWD intermittently won't shift out of Low. If I stop, shut off and restart the engine, it works fine. Transmission repair shop didn't find problem with transmission, but did find 2 wheel velocity sensor signal fault codes on the computer. What's wrong?