Closed Loop (Fuel Control)

After a cold start the engine runs in open loop, using stored values, until the sensors are warm. At full load the engine may switch to open loop again for protection. Live data on a scan tool shows the current loop status.

The control unit reads the sensor, compares it with the target and corrects injection continuously.

An engine that never enters closed loop often has a faulty coolant temperature or oxygen sensor. Fuel trims are only meaningful in closed loop.