I first became fimiliar with engine computers when I had installed a SilverLeaf monitor in one of my previous RVs.  When we moved into a class C I missed not having a diagnostic device to fill me in on various   check engine lights.  Looking online I came across the  ScanGaugeII which is designed for light duty vehicles and after a few months of use quickly decided we needed to handle the product line here at RVupgrades.   Since Diesel Pushers use a different engine software protocol I was without a vehicle computer unless I went with a Silverleaf system which was too big for my dash.  So when I heard a ScanGauge for larger Diesel vehicles would be available for my RV back in March I was ready for it.  Last Thursday our stock finally came in and I installed the unit just before a weekend trip and was glad I did.  The number one reason I wanted one of these units was to be able to read   engine fault codes.  When a check engine light comes on in a big diesel motor it generally means trouble and knowing how much trouble is invaluable in determining what steps to take.  In my case we were barely on the road and a check engine light came on and instantly the ScanGauge unit showed the error code.  I quickly read the code to my wife and she punched it into her phone.  Within just a few minutes we knew we had a non responding EGR valve which is an emmisions device and that the motor's horsepower would be derated by 25%.  Before we hit the next rest area she had a diagram where the part was located and possible issues, such as loose wiring.  I shutdown the motor, made sure all the connections where tight, fired it back up and all was clear.  I doubt I fixed it but it was so reassuring to know what the problem was and whether or not I needed to head for service immediately or continue on.  After that bit of excitement I checked out a few of the gauge readings available, and pretty much focus on the MPG and how much I can improve that by driving a little slower.  That alone will pay for the unit in no time!