Aftertreatment Control Module (ACM) monitors DEF tank temperature and uses it to control the Aftertreatment DEF Tank Heater valve to keep the DEF from freezing.
This temperature monitoring is also used to avoid stopped DEF dosing due to high DEF tank temperatures. If the DEF temperature is too high, reverse flow will be activated, if the temperature stays high for a short duration, a DTC is set.

Conditions for diagnostic trouble code (DTC):
1) DEF Temperature above 70??C (158??F)

Observable symptoms
1) No aftertreatment diesel exhaust fluid (DEF) dosage

Probable cause
1) Extreme driving conditions (High ambient temperature)
2) DEF Tank too close to hot object
3) DEF Tank heating valve stuck open
4) DEF Tank Heating Valve installed backwards
5) Aftertreatment diesel exhaust fluid (DEF) tank, Temperature Sensor