IM pretty sure I still have my catalytic converters. Do you ?

[QUOTE=sr3tlaw;3366301]Thank goodness I found this thread. Especially since it's the famous @blackoutt

Doug Thoroughly Short Headers installed, think we bought them from the same group buy a while back actually. I'm running the URD Rear O2 Simulator, 2UZ-FE V8, 2005-2006, Dual Channel (O2 Sim Type E) = $149.00 that was on backorder for a while. Here is a link to the plug and play that works with our 2UZ-FE 4.7 V8

Just recently, like, RIGHT before INSPECTION too some codes were thrown - P0172 and P0175. I have the @slyfox75 Secondary Air Bypass Installed a couple years ago and the instructions mention to tamper with the wiring that goes into the MAF sensor. Could the included relay he provided go bad? Idk, just thoughts

Are these related? Maybe the URD Simulator took a dump and needs to be replaced; or the relay included in @slyfox75 End of Quote

@sr3tlaw ,
I'll be glad to assist to help troubleshoot. I've never heard of a bypass relay failing in the field but everything is possible. It potentially can fail open or closed.(I would think closed would be most probable). If stuck closed, its as if you have no relay/bypass and correct ambient air temp would be sent to ECU. If stuck closed.....it would send a very low ambient air temp to ECU....which maybe could get you a rich code. We can test this with multimeter, or you can unscrew one red connector and hook it back to factory wire(remove bypass from circuit and make like factory) to see if that changes anything. I also happen to have a MAF sensor I can send you to use for testing if you'd like, just PM me. Also Techstream should show your air temp if you have it(that's probably easiest way to ensure its right).

Alright, lets look at this from a logical perspective. IF the slyfox bypass is installed correctly the only thing it will mess with is intake air temperature, therefore the bypass failing will not cause a MAF error and rich bank 1 and bank 2 faults (172, 175) without also causing an IAT fault. I've had my slyfox wiring come loose once after checking air filter, it caused an IAT fault, I fixed the wiring and it was resolved. I agree with slyfox that I don't think it's the bypass relay, they are quite simple and robust systems.

Now onto the simulator part.
You said you have the shorty headers, so do you have catalysts welded to them or straight pipes?
If you have catalysts welded to the shorty headers then no need for simulator unless you're logging p0430 and/or p0420 faults but not likely. Removed the simulator. Still logging faults? If yes then you have other issues such as an exhaust leak before the front O2 sensors, so maybe a gasket leak or bad install job of the headers? Or could also be a vacuum leak elsewhere, these usually flag some other faults as well though too.


If you have empty piping welded between the shorty headers and the y pipes then you need some sort of trickery on the REAR or sensors to prevent p0420 and/or p0430 faults. I was told by URD that the plug n play didn't work for our vehicles but I'm also assuming you have cats and don't need it anyway. It does not appear to be causing the issue because the faults that will log if it goes bad or is out of adjustment are the catalyst inefficiency p0420 and p0430 or REAR O2 sensor stuck high/stuck low, or slow switching. The faults you are logging are related to the FRONT or UPSTREAM O2 sensors. Which brings me back to.....do NOT install any spacers or simulators on the FRONT O2 sensors. This could very well be causing your issue. I know that DT and Jason B have been slinging misinformation about this but trust me those upstream sensors are seeing the correct exhaust stream just as factory without needed to be tricked. Any trickery of the front sensors will cause rich running p0172 p0175, poor fuel economy, and possible engine damage if ran long term. Send us some pics of where your upstream O2 sensors are mounted into your shorty headers and we should be able to resolve this question quickly.

Does URD make a PnP kit for us? I found an old link, but I can't find a current listing for the 2UZ.

Underdog Racing Development

@blackoutt @Drift Monkey

Swear this 0420 code is a yearly occurrence and only happens right before registration.

I'm running the OLD URD Rear O2 Simulator, 2UZ-FE V8, 2005-2006, Dual Channel (O2 Sim Type E) that was on backorder for a while. The same link posted by @Drift Monkey - thanks for that by the way. It was installed February 2016 when the headers were put in.


After desperation settled in; reached out to URD asking for guidance. Come to find out, there is a newer "Universal Simulator" they sell. But now I cant find it on their site! Below is correspondence from URD last year on the matter.

Also found this as a potential solution. Not sure what a mini cat is or if it could possibly replace the simulator altogether. Tagging @duffdog for this

I no longer manufacture the mini-cat. Too many people were using it inappropriately and I no longer wish to get complaints about how it doesn't work with blown engines, bad exhaust installs, etc. The original function was for passing smog in CA where there is no other possible solution to get your truck smogged. Other uses are not recommended for the mini-cat.

Wow that's a shame. I just want to pass inspection..in Texas lol.

I'll have to keep digging for a solution to this 0420 code

I am now in need of an O2 sensor for my 4Runner and I can't locate one on the URD website. I wrote them to see if they still carry it but don't advertise it. I'm suspecting that the EPA crackdowns on emissions has forced a lot of companies to stop selling products like the O2 sensor simulators. I will update the post with any response from URD.

I did have the defouler and that worked for years but it rusted thru and the O2 sensor was just dangling under my truck. Half the defouler is still threaded into the bung and Given the orientation of the bung, I can't get a drill up there to remove the rest of the defouler. If I can't get a simulator I guess I'll have to take it into an exhaust shop to get a new O2 bung welded in.

@black4vcobra
I'm really glad that last post I did got some traction. Thanks for your reply.

If it's not too much trouble, would you mind collaborating a bit on trying to get this nuisance taken care of? I do have relevant information from you RD dating back when I first got my headers installed and then another correspondence a few months back when the 0420 started throwing again sporadically. What's really funny is that while I know all of these shops can get in huge huge trouble for emission stuff and whatnot I just have a real strong belief that the nerds like us driving the Toyota 4Runners aren't really looking to pollute and **** up the environment we just want to explore LMAO
Can you shoot me a PM or an email to further discuss I'll post my findings on this thread once we get something concrete.

Hey, I tried to send a PM but not sure it went thru. I did hear back from URD as well but not what I wanted to hear.

I'll check in a bit to see if the message went through.

What did URD say?

To paraphrase, the E-P-A are a bunch of bullies to small businesses so URD does not have such a product.

@blackoutt
@black4vcobra
@duffdog
@Drift Monkey
@slyfox75

Are you still around? Resurrecting an old thread here, still having this issue to date (2022-05-23) and want to reassess.

Hope all is well!

Craig Walters

I’m alive

I haven't logged in to this site in a while. What I find is possibly the best and cheapest solution for the P0420 and P0430 codes is to take one of these:

Robot or human?

Put it into a lathe to make the hex part a circle, Drill out the exhaust factory Bung, slip this thing inside the exhaust so that it appears like a factory sensor bung, find a skilled welder to Tig-Braze the thing into the exhaust and replace your existing rear o2 sensors. Now, you have a replaceable sensor that looks like a factory bung and the braze can be melted off if you want to install something else. Also, you did not have to pay me $100/hr to manually make these stupid things on a lathe.