Carrier Performance Edge Owner's Manual page 51

You get a service reminder message
Service reminder messages - check UV light, check hum pad, check filter -
tell you that it's time to change the UVC lamp in the evaporator coil box
connected to the furnace (when installed), humidifier pad (when installed), and
furnace filter. Make the indicated changes with the exception of the UV lamp -
for important safety reasons, ask your dealer to replace that.
You
get a system
error message
Here are the possible system error messages and what they mean:
E1 The system isn't communicating properly. Call your heating and cooling
dealer for service.
-- The temperature sensor isn't working. Call your heating and cooling dealer
for service.
E4 There's an internal memory failure. Call your heating and cooling dealer for
service.
E5 The humidity sensor isn't working. Call your heating and cooling dealer for
service.