I have a vms el320 on a 1999 cummins ISC 8.3 and it wont read boost pressure,but if I hook up a cummins scanner that reads boost pressure and the vms will show the boost pressure.So why does it read with the scanner hooked up? Do I need to send the unit in for a software update? Will that cure the problem? The vms has the original software from what I can tell. 12RV10 2002 Thanks Ray