The injector driver transistor inside the ECU can fail, usually due to a shorted injector drawing too much current. This is more common on early R9M ECUs (Siemens SID307).
The injector on cylinder 4 fails internally – typically a shorted or open solenoid coil. Injector resistance should be around 0.2–0.5 ohms. An open circuit or extremely high resistance confirms a bad injector. renault df417
The vehicle may enter a "limp mode" to prevent engine damage, resulting in reduced power. The injector driver transistor inside the ECU can