How to force OPEN LOOP mode on OE ECU??

[YarisSedan]

If by open loop you mean when the computer is not looking at your o2 sensors and not in control of the fuel trim you could probably simple disconnect your engine coolant temp sensor to manually keep it in open loop. The ECU dosnt go into open loop till i think it measures thermostat open at 180 degrees or so. Not sure what the yaris reads when the ect signal is loss some cars it will just show hot and turn the cooling fan on all the time. If that dosnt work I would just buy a cheap ect sensor and just have it plugged into the connector sitting there while leaving the factory one installed in the car. It will read then the ambiant air temperature keep the cecl off and fool the computer it will keep it in open loop indefinitely until you plug it back into the stock one.

[maxthehax]

Originally Posted by YarisSedan

If by open loop you mean when the computer is not looking at your o2 sensors and not in control of the fuel trim you could probably simple disconnect your engine coolant temp sensor to manually keep it in open loop. The ECU dosnt go into open loop till i think it measures thermostat open at 180 degrees or so. Not sure what the yaris reads when the ect signal is loss some cars it will just show hot and turn the cooling fan on all the time. If that dosnt work I would just buy a cheap ect sensor and just have it plugged into the connector sitting there while leaving the factory one installed in the car. It will read then the ambiant air temperature keep the cecl off and fool the computer it will keep it in open loop indefinitely until you plug it back into the stock one.

Yes. By open loop I mean when there is no O2 reading.

I have a scangauge, I can see open/closed status, and I dont think it is always directly connected to the temperature readings. When the car starts at cold it's open loop by the time O2 gets hot, and I can see the closed loop arrive way before my car gets the 185 degree mark (85 celcius, operating temp).

...if by exemple the main O2 stop working for any reason, it should send no signals to the ECM (0 volts), WOULD'NT THAT FORCE THE ECM TO RUN OPEN LOOP?? Because I think this is what I experienced, but I dont know what caused the O2 to send no signals.

What I know is while the O2 sent no signal, I was running way too lean where normally I was perfectly fine. I were able to correct that by adding fuel in the map, where normally it changed nothing because the O2 was the main controller.

I think is it pretty hard to explain for me, but my main question is about how to get the car running permanently on open loop, so I can easely tune it without messing with the O2 again. Maybe you are right about unpluging the coolant temp sensor, but I doubt about it, maybe some1 else could chime in?