Why Is the Check Engine Light On in a Dodge Ram 2500 Diesel?
On Cummins-powered Ram 2500 trucks, the MIL usually illuminates because of emissions or fuel-system issues. Common culprits include EGR/DPF faults (P0401, P2459), fuel rail pressure deviations (P0087), boost leaks (P0299) and NOx sensor failures. Use a scan tool to read the exact code, inspect the related subsystem (EGR valves, DPF regeneration frequency, boost hoses, fuel pressure sensors), repair the fault, and clear the MIL with the scanner. After repairs, drive long enough for regeneration cycles and readiness monitors to complete.
If the MIL flashes or the truck enters derate mode, address the issue immediately to avoid aftertreatment damage.
Consult factory service information or a diesel specialist for recurring aftertreatment codes.