Volvo D12 shutting off while driving

Sounds like a grounding issue. I’m not sure what the mechanics did but for starters go too your battery box with the truck running and start wiggling wires.. EVERY single one of them to try to get it to shut off. Something could be loose or you might get lucky and clearly see the problem. If all seems good second thing I would check is go to your fuses. Pop open cup holder.. 2 Phillip head screws and it will pop out. With the truck running lightly... like gently wiggle those square relays and see if you can get the truck to shut off that way.

 

Those Volvo’s can throw codes in the Diagnostics that don’t show up as a pop up warning as well. Check Engine ECU and every category in Diagnostics.

 

On my truck this issue arrives when battery cables get loose.

 

If these are TEST DRIVES and no one an diagnose the problem readily.... it's time to move to the next truck.

 

With engine running wiggle wires all over the place .. on a cascadia I spent about 15k changing parts that numerous ships misdiagnosed . A mechanic said he knew the problem he started wigging engine harness and it stalled.. I would think that the same thing can be tried on a Volvo

 

Intermittent Problem is the hardest thing to diagnose. If you think it's electrical, I suggest you CLEAN your battery cables first and make sure they are tight, also make sure your batteries are secure. If you can borrow a scan tool you can test drive the truck and try to duplicate the problem and see if it log any code. and like every body else suggest to do wiggle test. 2006 model truck, I'm sure you are going to have wiring issue.
Good Luck and keep me posted.

 

Were you able to test drive with a scanner to see if any code will show up before it shuts off? An other suggestion is to install a vacuum gauge in the fuel system to see if it’s not starving for fuel.