The following components are connected to a common 12?V supply
R31: Aftertreatment Diesel Exhaust Fluid (DEF) Line Heater 1
R29: Aftertreatment Diesel Exhaust Fluid (DEF) Line Heater 3
A138: Aftertreatment Diesel Exhaust Fluid (DEF) Return Valve
A138: Aftertreatment Diesel Exhaust Fluid (DEF) Pump Motor
Y81: Aftertreatment Diesel Exhaust Fluid (DEF) Tank Heater Valve
If an abnormal voltage or current is detected on the common supply a DTC is set

Conditions for diagnostic trouble code (DTC):
1) Open circuit

Observable symptoms
1) Selective catalytic reduction (SCR) system does not function

Probable cause
1) Wiring harness
2) Connector