Cummins DTCs like P0087 (low fuel pressure), P0546 (EGT sensor issues), P0420/P2027 (DPF problems), P0335/P0336 (CKP sensor faults), and P0300 (misfires) indicate system issues. Diagnose using INSITE™, live data, and checks on fuel, sensors, wiring, and components. Fixes involve replacing parts, repairing leaks, or adjusting systems. Proactive maintenance and understanding system interactions prevent misdiagnosis and downtime.