Have a 2018 Blue bird all American with a Cummins. Bus set off alarms and derated the engine and driver was told to stop the engine. These are the codes 3712, 3714, 3251 and 5278. All related to the DEF system. Please help again.
If you have insite use the code analyzer to help with a full diag 3251 exhaust too hot, something is fueling the after treatment that should not 3712 information only codes active too long 3714 derate information only 5278 def system frozen either really cold where you are or the temp control in the tank not functioning properly Hope this helps
Bus needed for a run so was asked to check bus out and get to the bottom of the issues. My laptop said the Doser was frozen and had no heater for the DEF. So replaced the relay for the DEF heater and everything went away after bringing bus into the shop. went to move bus out ad warning for the DEF came on. Used laptop and got a 3258 saying no line heater. Checked fuse was good. I did notice 3 diodes. Could those be the issue? What is there another fuse for the system?