There is a Nissan Service Bulletin on the F-85 code problem,
It is SB2005-211. Issued March,21 2005

It has to do with the Fwd/Rev directional control boot.

It reads as follows:

NFC has recieved reports of an F85 code being displayed when the forklift is selected in the forward direction on a 2 speed transmission model. When this happens, the Transmission will be automatically placed into neutral, requiring the operator to bring the selector back to neutral , then to the desired direction.

We have investigated this situation and found the shifter boot may cause the lever not to fully engage.

If this is being experienced, NFC recommends repositioning the shifter handle boot inside at the the top and outside at the bottom grooves of the shifter housing assy.
( The plastic dash housing has 2 grooves to retain the boot edge, place the bottom of the boot at the bottom outside groove that goes all the way around the dash and the top has a half groove on the top inside near the inside of the dash.)

That's NFC's version,
We find most of the time that directional controls are being slammed or forcefully shifted by drivers and usually end up replacing the controller no too long after this issues starts showing up.