Originally Posted by PolkaPower
I was reading on a Cherokee forum and a guy with a 98 was saying that motor temp had nothing to do with the system going to closed loop and it was the temperature of the 02 sensors that determines that.
So even if the motor isn't up to operating temperature and the 02 heats up to spec, does it go into closed loop mode regardless of the motor temp?
When the engine and the O2 sensor reaches the "operating temperature". The FSM states something similar. I've searched, but have not found any more definite info.
In reality, it's probably a combination of factors that is programmed into the PCM: engine temp above a certain threshold (but not full op temp of ~200F, probably more ~ 130F), O2 sensor output above a certain voltage (there's no separate temp sensor in the O2 sensor), engine vacuum below a certain threshold (under moderate acceleration the PCM stays in closed loop) AND (in my experience) there's also a minimum warm up time programmed into the PCM.