Mainly the IAC and ECM
check for a bad fuse
Behind the battery on front (L)eft side.
replacement of lighter fuse in a 1998 q45 infiniti
There is a little box or cap in front of the shifter remove the cover and press down with a screw driver. Then check the fuse box and change out the fuse and you will be able to shift to reverse.
Mine is behind the little storage drawer on the left side of the steering wheel, you have to pull it all the way out.
incabin fuse box
fuse box cover
it not FUSE, ITS A CIRCUIT BREAKER
headlight fuse box for 2006 m35
fuse box cover
It is by the battery under the covers