Understanding & Live Graphing of the Rear O2 Sensor: OBD4Everyone Ep.19

Good job

Thinking the catalytic converter was a response to carburetors and early EFI and now that fuel metering is so advanced its now just a restriction that demands you waste fuel to keep it warm.

Hi, thanks for your video.

My O2 sensor 2 shows the voltage ranging from 0.6 to 0.7 consistently. Does this mean that the catalytic converter is not functioning properly, it looks like no catalytic situation. As a result, it seems to cause increased fuel consumption. Is my understanding correct?

Great video! I purchased a car with the Cat removed. It has a strait pipe with no 02 censor. Check engine light is on, but the car seems to be running fine. Should i try to reinstall the 02 into the exaust, or what are your thoughts? Thank you

Thank you for the video. It was very informative. Currently, I'm facing a problem with my truck throwing p0420 code which mean catalytic below efficiency. When i reviewed the data from both o2 sensors based on your video, my downstream o2 sensor constantly shows voltage reading of .8v while cruising at same speed. It goes down to .2v when i lift foot off gas. Should not it be close to .5 at cruising speed? Do I really need a new catalytic converter?

OBD Fusion should have a free version because most OBD apps don't work with certain cars so would be nice to just check if it works first.

I have a problem with me 2013 honda crosstour v6. The car has 186k miles and every 2 days map sensor like come up p1129. I replace map sensor, plugs, timing belt check for ground, replace ecm but the light keep coming. When the like come the exhust smell like egg and no power at all at full throttle the rpm slowly go to 4k before changing. I took my upstream 02 out and i start the car for 5 minute immediatly inside the cat i can see red cherry color and i dont have code for cat or 02 sensor. I check 02 reading and the guy who help say my cat is bad he say the cat hold power back am lost. Before i order cat i need your help or input thanks

what if i dont use o2 sensor rear...check engine be light?

Just want to know why my rear O2S reads about 0.2 volts when rpm rise?

As i know if the rear O2S switching from rich to lean that’s means the catalytic converter is bad , it should read study voltage about 0.5 volts. Am I wrong?

My O2 sensor bank 1 doesn't show any voltage. The wiring appears to be good. Should I assume this is bad or are there other ways of checking this? Thanks everyone!

Very knowledgeable information. Is normal to jump into open loop when descelarate and recover close loop just after step on gas pedal and recovering acceleration? O2S2 both banks stay on 0.8 mV and Fuel trims from that sensors stay on 99%. Any clue is everything normal?

Hey buddy, thanks for the video, appreciate it! I have been getting P0296 and P0420 for bank 1 (right side) on my 3.6 Grand Cherokee. I've checked rear and post cat sensors and figured out my CAT it dead (200k km), so I got Magnaflow California Legal universal CAT which everyone praises in forums to solve P0420. Indeed it helped, although P0296 did not disappear at all. I`ve checked voltage of post cat sensor Bank 1 plays between about 0.1-0.2v when driving steady, although bank 2 driver side (original cat) post cat sensor plays between 0.6-0.7v.

What do you think is the root cause?

o2 sensors don't detect o2, they detect HC and CO on the rich side of lambda 1. On the lean side of lambda 1 the sensor detects a lack of o2. The peak voltage after the cat is always less than the peak voltage before the cat. That's due to decreased concentrations of HC and CO. Likewise the minimum voltage after the cat is always more than the minimum voltage before the cat. That's due to stored o2 in the NOX. The switching rate is determined by engine speed. There's a time delay between air and fuel going in and exhaust coming out. No sensor can actually output 0.5v it will jump from about 300mV to about 700mV with no in between.

My Rear O2 Sensor Stays at 1.27 v in Idle condition but fluctuates around 0.7 - 0.9 Volts when running. I am getting three DTCs - P0172, P0130, P0420 at the same time. Please suggest what to do. My car is Suzuki Alto (2014).

have a 2002 jeep wrangler, just replaced bank2 sensor 2 and getting PO158 and P0161 codes, live data shows a constant 1.000 volts. Could it be the new sensor is defective or is it likely a shorted wire?

Hi, i have P0036 code heater control circuit on bank 1 sensor 2, i think this code showed up cause recently i have leaking coolant on cylinder 1 and 2 so i bring it to mechanic for headgasket replacement, now its running fine but when i check the misfire monitoring data , sometimes each cylinder has 1 misfire, but not all four of them together, every day i have 2 total misfire on random cylinder, it could be the faulty rear o2 sensor?

Hey got a 2005 Elantra gt I’m using a craftsman obd2 reader and the live graphing says my oxygen sensor voltage at an idle is 1.8-1.9 volts

My rear O2 sensor stays at 0,7 volts, I t does not go down much for sometime, I am running lean with +25% fuel trims

Hi, and congrats for your video. One question. I have a Mercedes clc 200, i have the primary cat removed which is in the exhaust manifold, and changed the second cat with a high flow 200 cel cat. He installed also an o2 sensor fooler with a minicat in the downstream o2 sensor in order not to have codes. Will i burn more fuel due to downstream o2 sensor fooler or have any other problem? Thanks

I have code p0171 lean bank 1 & P0171 lean bank 1 pending also right now. Scion tC 2006 - maf, air filter and oxygen sensor replaced. My reading (closed circuit) for my 02 sensor (Bank 1) reads at Volt output 0.740 to 8.00(v) My 02b1s1 says n/a? my EQ_RATB1S1 read at 1.002 with rpm at 2800-3000. in idle 02bs1s2 dopped to 0.015 (v)
My shorttf1 after warm up in idle 2.6 longft1 is 32.1
Rpm 2800-300 shortft1 moves -3.9 to 1.6 Longft1 stays at about 24%
I cant tell if there is a vac leak, 02 is bad, fuel injectors/spark plugs bad or fuel pump. From my readings I cant tell what they mean... vac leak, fuel pump or 02 sensor Any advice?
Side note the last 2 days just started with idle issue, hesitant when I press on the gas pedal. My throttle reads at 18% which is where I believe it should be.

Really good video! Thanks for explaining this so well.

I have no codes but a slight misfire and a bogg down when warm when I hit the gas bank one and two upstream are up and down bank one down stream is between .730-.750 but bank two downstream is between .025-.130

Hi, my rear O2 sensor stay at 0.9-0.8 volts all the time, it doesn't switch at all when I accelerate or decelerate, I can assume that it is a faulty sensor or I have a problem with air/fuel mixture? One more thing, my long term fuel trim is around -8%, I checked my first O2 sensor and seems to work properly. A faulty rear O2 sensor can cause this to fuel trim?

hi, hoping you can help
i had a p0141 (heater), changed o2 sensor and now my o2 sensor voltage is fluctuating,, 0 to 800mv, back to 0, 800, 0 ,800, 0, 800, 0 ... would you say the replacement is faulty? The cheapest branded part i can find is £60, whereas the one i bought was a whopping £18 lol. So assume it's just shit quality, i know you shouldn't cheap out on them and this is the first time i have but hey ho

So, the rear O2 sensor reading mostly 0.000 is bad? It reads 0.000 to 0.035. I just cleaned out the cat, as it was a bit dirty. It was giving the code for poor catalist system. 2013 Toyota Echo.

Healthy O2....like it took vitamins & no McDonalds for lunch?

I’m interested in installing an O2 on an older disse vehicle to look at AFR - is there a tool I can buy/rent to hook up directly to the O2 sensor to output that data? I’m not looking to have a permanent mounted gauge, I just want the data for tuning. Plus, most gauges don’t work for the higher AFR ratios of diesels

I just came here for an idea on the expected voltages so I can hook up a dual switch with different voltage dividers.

Ahh yes, the rear O2 sensor . That's the one that rats you out on you emissions test that your catalyst is failed. 😉

With the recent Cobb updates for WRXs I was looking to get tuned but worried about having the dreaded P0420 code as I bought an aftermarket Jpipe with a cat but not sure of if it will throw a code. I was told that it shouldn’t cause the code but if it does the rear 02 spacer should solve it. However several people have been telling me that the rear 02 sensor is used for long term fuel trims and other things that are needed. Based on the videos and others I’m not sure they are right. So my question am I able to use a 02 spacer without effecting anything like fuel trims or anything else?

Thank you for the amazing video. I ordered my elm327 adapter and will be downloading OBD Fusion for Windows. I am getting a P0420 on my 4 cylinder 2006 tacoma with only 95,000 miles and am trying to confirm that it is the "very expensive" Cat. This truck has an A/F sensor on the front of the Cat. Is the procedure you present in this video the best way confirm that it is indeed the Cat? Thanks again.

My downstream o2 sensor is reading 0V, replaced it with 4 o2 sensors and one From a dealership, its Still reading 0. What Could be the problem?

Helpful video. I didi use a BlueDriver to scan all my o2's voltages and ratios. I also have a V6 camry as well, but Toyota or not is not my question.

The graphs for both upstream sensors' voltages are very consistent with each other, however, the graphs for both downstream sensors' are different.

Bank 2's downstream sensor's graph seems to change steadily, kinda like hilly terrain.
Bank 1's downstream sensor's graph seems to rapidly fluctuate from 0 to 0.9 volts, kinda like spikes, or upside-down icicles.

Which downstream sensor is bad? I have replaced the catalytic converter on bank 2 due to a P0430 code, and that code went away.

Hey amazing video with great detail however im at a loss car was throwing code p0100 maf sensor replaced it engine ran so much smoother no more rough idle but now i get code p0170 fueltrim bank 1 astra h 1.8 2006
LTFT(B1) has a constant 11.7 o2s1 (B1) fluctuate between 0 and negative 25 o2s2 (B1) says negative 100 and doesn’t move any idea where to start i was thinking maybe o2 sensor is bad but im no car expert would be great full for any advice thanks in advance

I can't find answers anywhere. My O2 downstreams, even the new ones, are stuck around .7-.8V and barely respond to any engine reving, or driving. That should be rich right? Well, the LTFT are in positive double digits, indicating lean? It's both rich and lean??

Quick question because I’m curious if it’s my cats, or o2 sensors. So at a steady 50 mph, bank 2 fluctuates between .01-.8 while bank 1 stays at .72-.73 and doesn’t move. What could I be dealing with here?

Hi , very informative video. What software app are you using to plot the graph?

This video is insanely high quality. I really hope your content gets the visibility it deserves.

I've got a 2012 Toyota Corolla with about 115K miles on it. It has been well taken care of over the years by the previous owner, they changed the oil and such impeccably, had everything done on time, etc. As of the past couple of years, the downstream O2 sensor started testing only 1 or 2 out of the total of 5 readiness tests on OBD2, flipping between 1 and 2 out of 5 total tests for it and basically just halfway testing and untesting. I've checked voltage on the wiring, changed the O2 sensor 3 times in 2 years (Toyota-branded Denso made no difference vs aftermarket), had the battery tested, etc. When the ECU is reset completely, virtually all tests are complete the next day. It requires overnight testing for the Evap, but everything else tests very rapidly, including both readiness tests for the upstream engine-side O2 sensor. The catalyst also isn't testing, which I suspect is because of the downstream O2 sensor (before/on the catalyst) not testing first.

What could cause this? There is no check engine light, no error codes in the scanner or anything to indicate that anything is wrong. What am I missing? OBD2 device also shows the voltage of the downstream O2 sensor is registering and also it is reading the catalyst temperature properly. So I see that it is getting about 1V when the throttle is pressed, the upstream and downstream are talking to one another by adjusting fuel trim and such based on whether the throttle is being pressed, etc. Toyota recommended cleaning the throttle body, but that doesn't seem to be related to the downstream O2 sensor that we're having issues with. It's simply jumping back and forth between 2 of 5 readiness tests completed, then back to 3 or 4 out of 5 tested, then back to 2 or 3 tested and just says they haven't been completed yet. We've driven it hundreds of miles after reset. Same thing over again.

Hi, I have seen several Videos that uses an O2 spacer to remove the P0420 and P0430 codes. What does this spacer do? Just for my knowledge.

I have a 2021 Hyundai Palisade V6 and the above 2 codes are being thrown. How is it possible that both Banks come faulty at the same time? The car is only 10,000 Kms driven

Hi, my car has a po420 code and my o2 bank one sensor is negative so - 0.03. Is this faulty sensor. Thanks

Stupid question I have looked all over for odb fusion for PC and cannot find any legitimate sites. Who make this software or is this strictly for phones/tablets?

Now here's a mystery. I have a 2014 Mitsubishi Mirage that's getting a P2096 code for "post catalyst fuel trim system lean." However, the upstream wideband O2 sensor shows it's slightly rich the majority of the time, and the rear sensor voltage fluctuates between .54-.88, also indicating it's rich. But somehow, I keep getting P2096 lean code popping up repeatedly. This doesn't make any sense.

Great narration!

Cross counts - Thats what its all about. Its a secret ratio front o2/rear O2 crossover of .45 volts. What is it ????? who knows. 2/1…. 5/1….. 10/1 . Maybe A super smog tech has this secret ratio. The ECM is programmed to calculate the cross counts and trigger a fault if the ratio is too small. I would like to know what the ratio is!