I know that one is when the car is hot, and it uses all the readings from the sensors, and the other is when its cold, and runs off of certain set parameters, but can someone describe all the stuff to me in detail? I know its a dumb ? but I was jsut thinking about it today and got all confused about which ones which, and which sensors arent really used while its still cold and stuff. Thanks

 

Car goes into closed loop after it has been running for a bit, and is all warmed up, unless you are throwing a trouble code that keeps you in open loop (limp home mode).

 

in closed loop the PCM watches the O2 sensors. thery are watching these sensors to see if the engine is runing lean/rich. the O2 sensors cant do this until they are heated to 600 degrees F. when the engine isnt warmed up the PCM uses voltage signals from sensors such as MAF, MAP, TPS, ECT, IAT to control the mixture.

dont know if that helps, thats the short version, there is alot more detail, but i dont want to type,...

 

Open loop uses more gas. That's pretty much all you need to know.