Unless you are low on fluid, then Trace probably gave you the right answer - a bad sending unit. I went through this at the end of last season, my fluid level was fine so I swapped the unit and it's golden now.
The other thing it could be is a leak in one of your hoses. Dealer can check that for you. Replacing the pressure sensor/sender is less than 40 bucks if you do it yourself, and it's easy.
By the way, if the fluid level is low, fill it up via the dipstick hole with SAE 30.