Diagnostic Overview
Mack fault code SPN437514 generally points to a DEF/SCR dosing or reductant system condition that requires special diagnostic action. The SCR system uses DEF dosing to reduce NOx emissions, and this fault may indicate that the dosing unit, DEF pressure, DEF quality, or SCR control logic is not meeting expected conditions.
Likely Causes
DEF doser issue; DEF pressure problem; crystallized DEF; contaminated DEF; SCR sensor issue; module communication or wiring problem.
What To Check First
Check DEF quality, DEF pressure, dosing command, doser condition, and related NOx or SCR codes before replacing the SCR catalyst.