Most modern cars have computer systems that prevent the engine from straying too far into the redline by cutting fuel flow through the fuel injectors/fuel rail (in a direct-injected engine)/carburetor or by disabling the ignition system until the engine drops to a safer operating speed. This device is known as a rev-limiter and is usually set to an RPM value at redline or a few hundred RPM above. Most Electronic Control Units (ECUs) of automatic transmission cars will upshift before the engine hits the redline even with maximum acceleration (The ECU in a sports car's automatic transmission will allow the engine to go nearer the redline or hit the redline before upshifting). If manual override is used, the engine may go past redline for a brief amount of time before the ECU will cut power to pull it back or auto-upshift. When the car is in top gear and the engine is in redline (due to high speed), the ECU will cut fuel to the engine, forcing it to decelerate until the engine begins operating "below" the redline at which point it will release fuel back to the engine, allowing it to operate once again.