Oxygen Sensor Mod Issue / P0420

I performed the O2 sensor mod, attempting to resolve a P0420 code. I used a a 1megaohm resistor and 4.7microfarad capacitor, I'm confident it's wired properly (resistor in-line on blue, capacitor post resistor with negative polarity bridged to white). It is a newer O2 sensor, and there were no other codes besides the P0420 pre modification.

Post the mod, I am now getting P0136, and the CAT monitor will not set. I've read elsewhere that this RC combo has worked for some, but others have experienced that same as I.

Here are before and after snapshots of real time voltage output at low (1100) and moderate (2200) rpms (thanks to my buddy who lent me his snappy scanner). Post mod, the circuit caps the O2 voltage output to approximately 0.5V whereas prior it would go as high as 0.8V. Also note the erratic readings pre-mod at lower rpms.

Low RPMs, before:

after:


Higher RPMs, before:

after:


The mod seems to be doing what it's supposed to do to resolve P0420, with the exception of the new O2 code.

I've read that it may be more important to achieve a 1 sec time constant , so a 1uF may be more appropriate for the RC circuit.

Looking for advice from anyone who has been successful with this mod. As an FYI, my rig has CA emissions.

THANKS

 

It seems you caused a new code and a Heater circuit code will not be effected by your cheating to fix your PO420 code .

Was it when you were playing with the wiring or connectors maybe

Not being up close and in person you might want to figure out just why the heater circuit has low voltage.

Good luck

Remember the O2 heater circuit only works to the engine is up to temp I am sure you know this.

 

So the P0136 only relates to the heater circuit, and not the sensor voltage? I thought P0136 was for the sensor voltage...

PS - I'm pretty confident my mod didn't impact the heater circuit, I had an extra O2 sensor, built a duplicate circuit, and got pretty much the same set of results.

 

I'm not convinced you have a bad cat based on those plots. I tried the sensor wiring trick and got the same result. P0136 which is the sensor circuit. From what I can tell the modified circuit basically returns a steady voltage to mimic a functioning cat. Have you tried replacing the rear o2 with an OEM (denso) unit? That's what resolved my P0420. Rock auto had the dense unit for about 40 bucks.

 

https://www.obd-codes.com/p0136

it references the lean/rich condition after the CAT and not the heater portion of the sensor. This is probably not the answer you are looking for but I have bought and installed the URD simulator and have had zero issues.

getting the monitors to run has always been a pain... the monitors will not start if the CEL is on. If you already know this forgive me... fuel tank between 1/4 and 3/4 full. Vehicle has to be sitting overnight at least 8 hrs for the engine coolant temp and the inlet air temp to be within 10 degrees of each other and this has to happen twice. Normal driving after that usually runs all the monitors.

 

Yes, both sensors I used are OEM, one an original Toyota sensor that came from my prior Tacoma, and a newer one, Denso branded.
I had both installed (unmodified) previously, and had tried rotating them to see if that resolved the P0420, but with no luck.
Then I tried the mod on both...
I too am skeptical I have bad cats, but nothing I tried previously worked (swapping out O2 sensors, multiple doses of Cataclean, I even tried backing the sensor out by stacking multiple gaskets...)

 

Thanks for the confirmation on the P0136.
I have considered the URD simulator, but I looks like it's not available anymore?
And, yes, I am familiar with the drive cycle juggernaut... glad I'm not the only one I never been able to get all of them to close, other than just letting it happen on it's own, which takes forever and a day.

 

https://www.urdusa.com/rear-sensor-simulator/

web site says out of stock.

 

Thanks, I asked to be notified if it comes available.

Still hoping someone out there has been able to make the DIY version work...

 

Use a spark plug plug extension, universal #2 O2 threaded sensor and threaded to flange adapter.

 

Thanks, I haven't seen a threaded flanged adapter anywhere... where should I look?

 

So rather than actually fix what's causing the code, you masked the code with some resistors, and now you're getting other codes?

Weird.

 

https://www.lceperformance.com/Oxyg...leztLafPdGWsCrPuOgyc8x92bs07x5iRoCbA0QAvD_BwE
You may have to drill the inside of spark plug extension to fit sensor in

 

Did you clear the code between replacements? Or did you leave it and wait for the light to go out. Should put on new sensors, clear the code, run through the drive cycles and verify it comes back or not.

 

Codes auto clear when proper repairs are completed. Sensor codes clear within minutes after fix.

 

Why modify the o2 sensor?

tricking the computer will only make it run more rich?

waste of gas and now your engine light will illuminate and you’ll be in limp mode= wasting more gas

just repair the p420. If not. You’ll be creating a whole bunch of issues in the future. Plus that cat will be burned out

 

#2 is Oxygen sensor
No modifications to S1 which is Air/fuel on 2001 and up.
#2 doesn't monitor or adjust fuel ratios.

 

That was not my experience with this code. I drove many miles without the light going out. Cleared the code and it re-ran the monitor and has been good since.

 

Wasn't speaking to 2nd gen because this is 1st gen forum

 

Message received, and appreciated - as are all your replies to my posts I'm looking for a short term solution, to get by an inspections hurdle. Other posts / videos etc seemed to show this as a viable workaround, but if it's not, it's not. Just looking for clarity on that point.