There's a detailed set of tests in the FSM for the power transistor. They were too complicated for me, so I just replaced the entire unit. It didn't fix my code 44, which still plagues the car every now and then on the freeway
You'll have to reset your timing when the new CAS goes in. Be sure to orient the new CAS correctly. There's a mark on one end of the the thing that spins, which coincides with a mark on the end of the camshaft. Otherwise your ECU will think the timing is 180* the opposite.