Derate Active — Possible Fault Codes
Found 3 fault codes associated with derate active. Codes are sorted by severity — check STOP ENGINE codes first.
SPN 4334 FMI 7
DEF Dosing Valve Mechanical Fault
Cummins X15 • Component: DEF Dosing Valve (DMU) • J1939
SPN 520605 FMI 7
SCR System Mechanical Malfunction
Detroit Diesel DD15 • Component: SCR Catalyst / NOx Sensors • J1939
SPN 4375 FMI 7
DEF Pump Module Failure
Volvo D13 • Component: DEF Pump Assembly • J1939
⚠️ Diagnostic Note:
Symptoms can have multiple root causes. Always verify with a diagnostic scan tool before replacing parts. The fault codes listed above are possible matches for derate active based on SAE J1939/J1587 fault code definitions and OEM service documentation.