SPN 5246 FMI 15 indicates an SCR (Selective Catalytic Reduction) system fault with derate active, often caused by issues like DEF quality, sensor failures, or exhaust aftertreatment problems.
First check DEF quality and levels, inspect SCR system components for damage, verify NOx sensor operation, and reset fault codes after repairs. Severe cases may require dealership diagnostics.
While possible, continuing operation with active derate may lead to reduced performance and potential engine damage. Address the issue promptly to avoid costly repairs.