2006 XC90 fan kept going after engine shut off. normal driving w/ AC on, hot weather. Had to turn engine back on and shut off again to get it to stop. What gives??

 

Standard feature called AfterBlow designed to dry out the evaporator and ducting to prevent corrosion and mold. It may cycle on/off several times for as long as an hour+ after the car is turned off. It also monitors battery voltage so as to not run the battery down. Nothing to do. Just let it do its thing.

 

Thanks PKRFACE! Also, can I remove the plastic panel under the engine compartment and leave it off, will it hurt anything?

 

There are 3 basic benefits to that panel. Better aerodynamics for better fuel economy and it catches minor fluid leaks so you don't leave spots on the garage floor or driveway. It also ties in some of the other plastic panels/shrouds and holds it all together. Best if it is left in place.