OBDII Automotive Articles
 
Difference Between Open Loop and Close Loop

Difference Between Open Loop and Close Loop

When starting the engine cold or there is a malfunction with the engine O2 sensor (or A/F Sensor) the Engine Control Module (ECM) will control the engine's air/fuel mixture in "Open Loop" which means that the ECM will use predefined parameters set by the factory to control the air/fuel mixture to the engine. Once the engine is warm up and there is no malfunction with the O2 sensor (or A/F Sensor), the ECM will start controlling the air/fuel mixture in "Close Loop" by using the feedback signals from O2 sensor, coolant temperature sensor, and other engine sensors.

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