I got the similar issue on the D5WZ heater on my 2005 Sprinter 3500, heater won’t start when turning on the heater booster switch, AP200 scanner reported 0802 / blower motor has open circuit fault code. I decided to depot the control module since the other heater parts are in pretty good condition.
Long story short, I depotted it, cleaned the potting material pretty good from the PCB and the components, and started to test it on my bench, very similar to OP’s experience, the motor started to spin and the controller is working now. I rigged it to the van with the motor/controller + burner without the heat exchanger and it does ignite and create flame. I will need new gaskets to put everything together. I think I will just run it like this without potting the controller to see what will happen.
The BTS247Z is a N-channel FET device with two temperature sensor outputs, pin2 and pin4, pin1 is the Gate of the FET which should get control voltage from the microcontroller, probably thru a buffer stage. The slanted part on my board has different marking, 422 U3D, it is a Vishay rectifier, basically a diode.
Here are a couple of pictures, I was able to taker out the PCB without opening the back of the controller housing.