Also, you by chance do not leave the PAS in city mode do you because that can cause it to overheat and cut out.
Ha! Where's that coming from, John? I've had mine constantly in CITY mode for 3 years now, should I be worried?
Look for something that will cause voltage to drop too low ie battery, bad battery to engine earth (very common), poor alternator charging. a too low voltage or no alternator output will cause power steering to drop out