Air/fuel ratio sensor testing thread

Lowboybrian wrote: So question... is the heater circuit the only thing that can be tested by taking an ohm measurement of the heater? And also verifying the 3.3 and 3.0 (toyota) voltages on the signal wires? Curious if any other part of the sensor can fail or slowly deteriorate that may cause inaccurate readings? I tested 2 different toyotas just trying to get a sense of what I should see but they are different. 2016 Corolla AF voltages go to 4.96 v (lean) on decel fuel cut and about 2.5 v at WOT. 2002 Sienna (V6) both AF voltages barely get above 4 v and between 2.5 v and 3 v at WOT. The Corolla downstream O2 reacts exactly as I would expect with each however the Sienna downstream is kinda all over the place because it rarely goes into the decel fuel cut off. It reacts as expected during WOT but doesn't go into an open loop drive/ decel fuel cut unless at high speed/rpm. Maybe thats just a difference in the ECM strategy from 2002 to 2016?... or would an aging AF sensor show itself in the form of voltages not going as high or as low as they should? The Sienna has a Cat Efficiency code that pops up every few months or so which is why I'm trying to get a read on the downstream sensor.... and the possibility of the AF sensors/ decel fuel cut issues contributing to this condition? No driveability concerns... just trying to learn more about their operation. Sorry I'm so long winded.... TIA

Fuel control with wideband sensors have improved over the years and is generally pretty tight on modern Toyotas. Sensors and cats both detoriate with age. the cat on a 2002 car is either going to be aged or been replaced with an aftermarket or possibly even de-cated. With a cat effiency code my first move would be a cat oxygen storage efficiency test.

Oxygen storage looked ok compared to the Corolla which was really only about 1 sec. And not seeing the normal oscillation pattern on the rear O2 for a bad cat. I'm seeing the rear 02 going a bit wonky because of the decel fuel cut issue I think but wanted to make sure I wasn't missing anything with AF sensor voltages since I'm not as up to speed on those sensors as I'd like to be. The decel fuel cut should return to fueling at 1200 rpm according to service data but its returning between 1800-2000 rpm and its at this point the rear O2 has more rich to lean movement which I'm just guessing might be what the ecm is interpreting as an efficiency issue? But regardless I don't want to clog this great thread with trying to troubleshoot that... My main concern here was making sure I wasn't missing anything on the testing of an AF sensor and if lower/higher than normal (whatever that is) voltages possibly indicate an aging or failing sensor. I have 4 other Toyotas here, 2 being close to the same vintage that I'll test when I get them repaired. I'll start another thread on this tho. Thanks bro.

This is a really cool topic to explore because there aren't exactly simple and easy, standardized tests out there for these sensors

There isn't a standardized test for a simple O2 sensor either

We like to think there is, but O2 sensors shift in value over time. Both directions. Misfires can also cause an upstream O2 sensor to switch at a non lambda value.

Great job Tyler !

OEM's can vary widely in how they display the signal from their air/fuel ratio sensors. Some use current, others use an interpreted voltage

Hope you don't mind a small point here...

[as long as this isn't generic data]

I believe its the other way around. The voltage is the internal measurement and the amperage is the calculated value. The amperage is determined by measuring the voltage across a calibrated resistance and doing the math.

The reason I point this out is that, for some, the term "interpreted" means you can't trust it. I run into this all the time in developing and delivering training. It can, and has, made for some uncomfortable moments in a class.

The generic side of this is very different. The OEs have to scale the actual numbers to match the sometimes ambiguous scale required on the generic side. That's regardless if they report in current or voltage. Its ugly