3VZ O2/ECU question - Toyota Nation Forum : Toyota Car and Truck Forums

thaharlequin · 01-12-2011, 04:07 PM

If both upstream O2 sensors were disabled, would the ECU use the downstream sensor to help adjust fuel trim and keep the car near stoich, or does it just revert to open loop and run whatever the default maps says to?

camry6 · 01-12-2011, 08:29 PM

It will run open loop until ALL sensors are working.

thaharlequin · 01-12-2011, 08:59 PM

Good to know, thanks!

thaharlequin · 02-15-2011, 02:22 PM

I'm bumping this because it looks like, at least for CA versions, that it will run in closed loop to some extent even if the downstream oxygen sensor is the only one hooked up. I leaned out the AFM a ton (8 clicks or something), unplugged the two upstream sensors, and the damn thing surged like you wouldn't believe, presumably because the downstream sensor was detecting the lean condition and the ECU would richen the mixture, then back off as it got too rich. Rinse and repeat. I even had the cruise control on at ~60mph and I could feel it surging. When I unplugged all three w/ the AFM in the same position there was no surging at all.