I believe the E4 code is low voltage. Shut the breaker off, unplug the unit then plug it back in then turn the breaker back on. The EMS should reset itself. If it doesn't, call Progressive tech support. I must tell you though, this is exactly what happened to mine. Tech told me to fill out a warranty claim online. I had a brand new one in less than a week.
2012 Eagle 320 RLDS
2017 Ford F-250 FX4 Crew STX 6.2l