An electrical switch that sits on top of the tranny. It is
connected, via a cable, to the shifter in the center console (why the
switch is not in the center console is another issue). The transmisison
takes its input as electrical signals so the PNP converts the shifter
position to the correct electrical signal. The PNP uses mechanicl
contacts and it is packed with grease. Apparently, over time, the
contacts have some problem and as it gets cold the grease may not do
its job. So, first cold morning in winter a lot of people have a
problem with the PNP switch (indicated by the flashing arrow on the
dash).

My former indy mechanic replaced about 20 a year (so he says).