o2 sensor simulator ie. diode or resistor fix for p0420 and p0430 error codes

[NoService]

hi guys its been a while

im looking for a learned member who knows his shit about electronics and how to make these 02 sims or cel eliminators

i know the rear 02 sensor ranges from 0.1v to 0.9v with a bad or no cat and around 0.5 to 0.7v slightly wavering being the sweet spot to make the ecu think the cats working normally

ive read conflicting over seas info online to use a capacitor a diode OR a capacitor and diode in tandem

what i need is way to make the wild 0.1v to 0.9v swings in volts being sent from the o2 sensor to be stabilized to around 0.5v to 0.7v

having no knowledge in capacitors diodes and such im looking for some guru here to help me solder in the correct whatever to be able to achieve this

reason i need this info is i have installed an aftermarket exhaust and my engine light keeps coming on with catalyst deficiency below threshold , but its just because i now have high flow cats

thanks
NS

[Uncle Fester]

Sounds like you need a low pass filter to smooth out those wild swings, can't see what a diode would be good for here.
Something like this:



The polarity depends which way around you have the wires, so if you can measure with a voltmeter the positive side, that is where the + of the cap and the series resistor goes.
You can also get a ceramic cap 1µF (or more parallel if it is still to wild) then the polarity doesn't matter.

... and as always DO AT YOUR OWN RISK !

[NoService]

this is the exact info i was looking for, clear and concise.

many thanks unkie fester you legend

NS

[Skepticist]

If you were wanting to 'fake' a good stable voltage then a forward biassed silicon diode (with a series resistor) should provide a constant voltage in the desired range. Not that I'm suggesting using such a solution of course.

[Uncle Fester]

If you were wanting to 'fake' a good stable voltage then a forward biassed silicon diode (with a series resistor) should provide a constant voltage in the desired range. Not that I'm suggesting using such a solution of course.

If you are suggesting to replace the cap with a diode to limit to 0.7V, that will not stop the voltage from suddenly dropping all the way down to 0.1V and it will still behave 'wildly'.
He wants the swings but they need to be more gradual and that is best achieved with a low pass filter.
A forwards poled diode parallel to the cap would avoid it swinging to 0.9V if that is a problem but together with the 1MΩ it might limit only to 0.5V and a lower resistor with much larger cap might interfere with the impedance of the sensor which is an unknown here.
The way I see it, the low pass filter without diode should smooth out those 0.9V spikes while avoiding it going down to 0.1V. If it doesn't, add a larger capacitor but keep the 1MΩ resistor.

[Skepticist]

If what's required to make the ECU happy is 0.5V-0.9V referenced to ground then my suggestion was that it could be simply generated without an O2 sensor at all if one were so inclined and oblivious to emissions regulations.

ETA Didn't recognise you at first Mr Adams (The avatar jogged my overworked memory cells eventually)

[Uncle Fester]

If what's required to make the ECU happy is 0.5V-0.9V referenced to ground then my suggestion was that it could be simply generated without an O2 sensor at all if one were so inclined and oblivious to emissions regulations.

It is not that simple. If you want to simulate a missing sensor, then you need to simulate a 'wavy' signal. You then might use a timer circuit to create slow pulses and again use a low pass but this time higher order to create what might looks like a triangular or near sine wave signal with an amplitude of 0.2V and a DC offset of 0.5V.

But this is not what is mentioned in the OP.

It is about a different exhaust system causing an erratic sensor signal.

ETA Didn't recognise you at first Mr Adams (The avatar jogged my overworked memory cells eventually)

LOL, I left the old avatar for that reason. May change at a later date.
I actually could bring a 60watt fluoro tube to fully glow in my bare hand when I was a teenager.

[Godzilla]

Ive regularly had to deal with this with aftermarket exhaust systems and "test" pipes in place of the cats.

Simply run a spark plug non fouler, you can piggy back them for extra effect.

I usually put 2 together and run the second o2 sensor into it.

It works by pulling the second o2 sensor out of the direct stream of the exhaust.

[NoService]

thanks everyone...im going with festers fix first (cheapest easiest) it that fails for any reason ill revert the wiring and install a set of minicats
they are what godzilla describes only with a tiny catalyst inside to fool oz sensor that everything is good
i dropped into a local exhaust place and told him whats happening , he whipped out a minicat and said you need two of these.
at $85 each i immediately thought of festers wiring genius and the price of caps and resistors, lol
the way i see it a couple of bucks ventured could mean a few cartons for me instead of the exhaust dude getting my cash
so ill be at jaycar 1st thing in the morning buying bits and hopefully the bottle o a little later on in the day

ill let you know how it turns out
thanks for everyones input
NS

[VroomVroom]

what sort of engine is this on ? turbo or non turbo ? Is it a narrowband or wideband sensor you are trying to eliminate? you gotta be careful doing this becuase if the engine ever goes over rich or over lean for any reason the ECU wont pick it up and compensate.
The rear sensors are usually more a Lambda sensor than an O2 sensor and they work differently.

[NoService]

vroom it is the rear post cat sensor .... the car does not use the rear sensor for fuel trims it uses the front one.....some newer cars use both but my old girl does not.....the rear sensors only reason for existing is to monitor emissions and to throw the engine light on if it falls below a 95% threshold......running high flow cats confuses the sensor into thinking the cats are cactus or missing....they are brand spanking new....im not the only one who has run into this issue thats why the exhaust shop sells mini cats but im doing this trick first as a lot of people have said it works a treat online and im all for saving $$$ if possible.

NS

[Godzilla]

No, the ones im talking about cost much less and do exactly the same thing.



You can stack these one one another, i usually use 2 at a time.

The idea is that you get the O2 sensor to read much lower gas emmisions by pulling it out of the gas flow, note the small hole and note that the more of these you stack on each other the further away you are from the stream.

You dont want to go too far out, just enough to stop triggering the O2 check engine light.

Some people even add steel wool into the holes to restrict flow into the sensor.

[NoService]

update time

ok i purchased 2x caps and 2x resistors as advised by fester (thanks mate)
wired them in as shown
took car for a drive to monitor the new rear o2 voltages using torques live data features
voltages from both banks have gone from the wild sharp swings between .1v to .9v to a slowly fluctuating voltage (see graph below) perfecto!!!!
total cost was $1.65 and an hour to do......rear sensors in my car are almost impossible to get to

so anyone else facing the same issues with either an aftermarket exhaust or even buggered cats can use this fix to turn off that pesky engine light
ive no doubt godzillas method will probably work too like the minicats but i literally cant get to the sensors without pulling other things off.....wiring was much easier for me in this instance

heres a graph showing the difference between the wildly erratic original signal (green) and the one calmed down by the low pass filter (red) a way slimmer range which the ecu likes



regards
NS

[NoService]

2nd update

after driving car for a few cycles the engine light reset throwing a o2 sensor performance error code....it seems the 0,4v the filter was throwing was not what the ecu expected to see afterall

a bit of research told me the ecu liked 0.5v or there abouts ....a quick chat with fester and he advised soldering in 2x resistors and 2x capacitors "in parallel" to bump up the voltage , which i of course screwed up and done them in series...it didnt work obviously

once fester confirmed i was indeed an idiot he showed me what parallel means i re soldered them in correctly, the volts jumped from 0.4 to 0.5v, the ecu seems happy with that

i have now logged 300klms and the ecu is clear of codes and i haven't seen that damn engine light for a few days now

so if you do this and get an 02 sensor performance error try bumping up the volts in increments till you find the sweet spot

hopefully you'll hit it first go

again i cant thank fester enough

NS

[Uncle Fester]

I suggest to stay in the range 220kΩ-470kΩ for the resistor and 4.7µF-2.2µF for the cap.

The input impedance of the ECU appears to be around 2MΩ and from what I could find, O2 sensors vary between 10-150µA at 1V max, so worse case Z=100kΩ.

If a higher voltage is required(up to 0.6V) use a 220kΩ resistor with a 4.7µF cap but this puts a bit more load on the sensor, which just means it takes longer to charge the cap after a dip.

[DarthV]

Good day, sir! You are clearly the "go to" on this topic and I had a couple questions, if you don't mind.

I have a 2023 Cadillac CT4-V series(2.7L) and have the same O2 sensor issue; I'm running a high flow downpipe. I used your schem and the 0420 CELS are gone, but Now I'm getting a P0138, indicating that the senor is reading too high of V. 1.1V, to be exact. Would I want to ad another 1M ohn resistor to bring this down or another 1M ohm R and another 1uF C?

I thank you in advance and truly appreciate your time and knowledge

Cheers from the States!

-JG

[diehardcat]

2nd update

after driving car for a few cycles the engine light reset throwing a o2 sensor performance error code....it seems the 0,4v the filter was throwing was not what the ecu expected to see afterall

a bit of research told me the ecu liked 0.5v or there abouts ....a quick chat with fester and he advised soldering in 2x resistors and 2x capacitors "in parallel" to bump up the voltage , which i of course screwed up and done them in series...it didnt work obviously

once fester confirmed i was indeed an idiot he showed me what parallel means i re soldered them in correctly, the volts jumped from 0.4 to 0.5v, the ecu seems happy with that

i have now logged 300klms and the ecu is clear of codes and i haven't seen that damn engine light for a few days now

so if you do this and get an 02 sensor performance error try bumping up the volts in increments till you find the sweet spot

hopefully you'll hit it first go

again i cant thank fester enough

NS

Hi!

Please look at the attached picture





Is that what you mean when you say you added '2x resistors and 2x capacitors "in parallel" to bump up the voltage'?

Thx!