587 miles to E on def and check engin light pops in to say hello. i top her off and 40 miles later i realize that ive got as much gittyup as a little 96 model 6 banger sanoma and the light is still on. code reader showed nothin. whats goin on here????
DEF heater failures are somewhat common especially through the first few years of production. Less common is a failure with the dosing line heater. Either can set code P20BA. To properly diagnose this you need to be able to perform a Key On Engine Off (KOEO) Self-Test and Key On Engine Running (KOER) Glow Plug Monitor Self-Test. The heaters are controlled by the GPCM. Depending on the results you would test the resistance of the heaters and their circuits. At the very least inspect the dosing line, wire harness and connectors for damage, corrosion and damaged pins. The reason the fault is detected when it's warm out is that the system, like all of the module controlled systems in your truck, will perform self tests on the system sensors and output devices and monitor for circuit faults.
If you are going to fire off your parts cannon and take an educated guess from the Internet, throw a DEF tank reservoir assembly at it. It contains the level sensors and the heater.
F.Y.I. Your truck feels like it has a loss of power because it is operating in derate mode due to the fault. This is normal and will not clear until the fault is repaired and the code successfully cleared.