Diagnostic Overview
Cummins fault code 428 is commonly related to water-in-fuel detection or fuel quality monitoring. The ECM may detect water contamination in the fuel system, which can damage injectors, pumps, and high-pressure fuel components. Causes include water in the fuel/water separator, contaminated fuel, failed water-in-fuel sensor, wiring issues, or poor maintenance of the separator. The first steps are to drain the separator, inspect fuel quality, replace filters if needed, and verify the sensor circuit.