There is a switch to control this coil and the switch connects ground from the pf back thru the aux ps and then to the CPU to the nor input. Start by checking for a ground at the switch and see if the ground is passed thru the switch when pressed. Then check for the ground going in and out of the aux ps and then back to the CPU.

An open diode will allow voltage spikes to travel around many boards and may cause strange things to happen or damage some items. A shorted diode will allow a higher current draw thru a transistor that it was not designed for which will damage it. Post a pic of the lane switch which controls the coil in question.