When the aftertreatment selective catalytic reduction (SCR) system operates under normal conditions, the aftertreatment control module (ACM) monitors diesel exhaust fluid (DEF) dosing valve duty cycle and DEF pump control value. When the DEF dosing valve duty cycle increases above allowed threshold and the DEF pump control value decreases below expected threshold, the ACM stops DEF dosing and reports a fault. The fault might be indication of electrical failure or blockage in DEF dosing valve or DEF supply line from the DEF tank.

Conditions for diagnostic trouble code (DTC):
1) Reduced NOx conversion
2) Observable symptoms
3) Too high NOx emissions

Probable cause
1) Clogged muffler
2) DEF Dosing
3) DEF concentration
4) Faults causing leaking or high hydro carbons in muffler
5) Aftertreatment Hydrocarbon Doser, over-fueling