Toyota AFR sensor Urgent help

Dears,

I want to diagnose Toyota Yaris 2012 with low power and high fuel consumption. Things I got from scanner

1- Long range activity from Upstream sensor : fluctuating between 55mv - 900mv. It is not running little lean and rich to be at stoichio. Upstream sensor should be playing little lean and rich to maintain stochio. How come this?
2- Short Term and Long Term are in reasonable range in Idle and underload.
3-Upstream is very responsive to propane gas and it enters rich condition.
4- Dirty maf cleaned still the same.
5- downstream sensor malfunction.


Any guide to component to put under monitoring for this issue?

I'd suggest watching the upstream O2 and Engine Load while at wide open throttle through first and second gears. The O2 should go over 800mV while at WOT, and the Engine Load should go to 85% or higher. If the O2 doesn't go rich at WOT, then the engine is running out of fuel. If it does, then look at the Load. If it's low, that'd suggest a breathing issue.

There's tons of SD videos out there for low power complaints. This one might be a good place to start:



For reference, this is the flow chart I follow for low power complaints:

Dear Tyler,

Thanks for your quick response. what I mean is " the O2 sensors become rich and lean at wot" if you watch the video closely and aim the o2 sensors, you will see o2 sensors fluctuate between 50-800mv. How come at WOT the engine o2 becomes lean with good fuel trim?

Thank you again

"How come at WOT the engine o2 becomes lean with good fuel trim?"
WOT should be open loop so doesn't depend on fuel trim.

Doesn’t an AFR sensor read the opposite of a normal O2 sensor. Meaning the voltage drops on an afr sensor while the voltage on a regular O2 it goes to max voltage

Snap throttle test should give a very distinctive signature from the AFR
www.linkedin.com/pulse/afr-sensor-inheri...rth-mandy-concepcion

Andy thanks for the Link in info.
So to appears that .5v is the equivalent of 2.4v and .8 equals 4v in Naros812000 example of A/F sensor range, .5v being lean and .8v rich.