VOLVO D12 strange problem

does it idle good and do you have any kind of fault codes

 

do you have a TAS switch on your Dash board

 

This might be a tas issue there is a sensor on the trans telling tas if the truck is in neutral when it is suposed to work, and when it does work only on idle it is supposed to shut down the truck and be able to start it up again when the engine temp drops and the cab temp drops saves you a lot of idle time in the winter but if they go bad they make these kind of issues i have bypassed them a few times but they are a ##### cuz they have a certain switch sequence in a box in the dash that you are supposed to flip to shut them off, problem is i dont remember what this sequence is, the other way there should be a sensor on top of trans telling the tas when the vehicle is in neutral try to remove this sensor and see if it does the same thing, sounds like this issue is coming from there to me. if you looked at the top of a thirteen speed before you only have one reverse switch on top cover sometimes mounted in the back or back and on the side, anything else on the top cover is extra try to remove this all together and see if this is your problem, that's best i can suggest.

 

https://docs.wixstatic.com/ugd/dba2a4_670998da37a448bd9bc33360c62e3fb0.pdf go to this link this is the system they have installed on them maybe they can tell you how to disable it this is best i can find on it.

 

so i found the number for the tech support for the TAS system you need to remove the box which is behid the pocket in the middle of the dash remove the cover from the box and give him a call tomorrow his name is stormy number 309-472-0676 he might have you take a pic and send it to him so he can give you right sequence