Phil- The PDM is not programmable, it is simply a distribution panel w/a few switches. You should have the LEDs lit or not according to the photos in this thread
. So there is nothing in it that will make decisions about step extension or retraction. There is a relay ahead of the Step Motor1 & Step Motor2 outputs that make 12V available on those two wires, but the same relay lights LEDs 7-12 (including the 9 & 10 for SM1 & SM2). So if all 7-12 LEDs are still lit when your step craps out, & you can verify there is actually 12V going out on those two circuits, the PDM is OK. If LEDs 9 or 10 die out when the step moves the one time, there is likely a problem w/the PDM; if its the relay internal to PDM i'd expect to see all LEDs 7-10 go out.
Have you verified that the step closes if ON/OFF switch is OFF & door is closed? Step closes if switch is ON, step out, door closed, then engine is started?
Step is closed, switch ON, door closed, then step opens when door is opened?