Check Engine Light On? ECU Fault Diagnosis & Repair | UK-Wide Service Is your check engine light stubbornly lit? While it could signal various issues, a consistently illuminated light can point to a potential ECU fault . Although Engine Control Unit (ECU) failures are less common than issues with components like spark plugs or sensors, they are serious and demand expert attention. A faulty ECU can trigger the check engine light , accompanied by symptoms such as engine stall