Oxygen Sensor Readings?

[Nick Bruns]

Hi everyone. Eric, you’re amazing. As busy as you are and still getting into the forum! Props.

(02 Subaru Legacy 2.5, auto with 128xxx mi) A bit of a head-scratcher for you guys. I took the plunge and bought a Bluetooth scan tool. I got it to originally diagnose a P0420 and clear the code to see if it would come back and to check the 02 sensor function to see if the cats are bad or it’s a bad sensor or something else. I cleared the code 5 days ago and it hasn’t come back. Well I am having some confusion as to which 02 sensors the scan tool is reading. (see the pictures).

One is “02 sensor 1 wide-range voltage” and “02 volts Bank 1 sensor 2.” The values for them don’t make any sense. The first one reads on average 1.3-1.5 volts (it fluctuates) and has gone up to almost 2 volts (way too high). The second sensor is a little more “normal” it reads under 1 volt consistently but also bounces around from .8v and under. It’s confusing because they seem to read higher than they should? Also, why is there no value for “02 volts Bank 1 Sensor 1”? I ran a graph of live data and it shows pretty much the same. Under 2000 rpm’s the wide-range sensor goes all over the place rich-lean and the other sensor acts like it should for a downstream sensor, fluctuating slowly and consistently, just the voltages seem wonky.

I hooked the tool to my wife’s car (’99 Ford Escort) and the sensors seem to be in order (bank 1 sensor 1, bank 1 sensor 2). Is this a Subaru-specific deal? Anyone else seen this before? Can someone help me interpret what is going on? “Also, what is the equivalence ratio”?

Thanks!

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Topic

[college man]

The bank1 sensor 2 is the downstream o2 and is reporting that the cat is
below threshold and not cleaning. So the o2 is working and reporting.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Nick Bruns]

Thanks for the info! Are these readings normal? I remember watching Eric’s video (and others) on the P0420 on his 90’s Subaru and the Odssey and the sensors shows voltages sometimes well under 1v, like .300mV-900mV. Also, what’s the wide-range voltage? I’ve never seen that before? So far the MIL hasn’t come back on so that’s good because the replacement catalytic converters for this car are sold as a unit and is $1000+ :blink: I have heard that the Subaru cats last a very long time and don’t go bad unless something else causes it. I did do some recording of sensor data and the waveforms looked good when the car was driving at a steady speed around 2000 rpms.

[college man]

Usually the cat o2 voltage will hover around .5v give or take.

[Author]

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