Code P0420

Post by **jsando2** » Sun Oct 17, 2021 7:38 pm

Okay! I replaced all my (4) upstream downstream 02 sensors, both catalysts converters, spark plugs, three coil packs all the exhaust is new and Im still getting Code P0420. Also Im getting the code for the fuel sensor but here is where my question comes into place. Can a code for the fuel sensor trigger a P0420 Code? Hummm, What else can I do to get rid of this code I wont pass emissions and Im late.

Post by **VStar650CL** » Sun Oct 17, 2021 8:01 pm

Dunno what you mean by a "fuel sensor" code. If you mean the A/F sensor, then yes, a faulty one can cause a false cat efficiency code. Other possible causes are an exhaust leak, plenum gasket leak, or a replacement cat that isn't as efficient as the original. The latter is common with cheap replacement cats, and most people end up putting a spacer on the rear O2 to kill the code.

Post by **jsando2** » Sun Oct 17, 2021 8:22 pm

Yes the A/F my bad, I just took it to a muffler shop to check for any leak and is all good, I guess is the cheap cats, I will try to place a a spacer on the rear O2 and see if that works! Do you know a good website to get it?
Thanks

Post by **VStar650CL** » Sun Oct 17, 2021 9:32 pm

There are tons of them on both eBay and Amazon for as little as $3, both straight and angled. It's not the sort of product where quality or materials matter much, but to avoid future issues put some anti-seize on it just like you would with a new sensor. Put "O2 spacer" in the search bar and you'll get thousands of hits.

Post by **jsando2** » Sun Oct 17, 2021 9:38 pm

Yup just got a couple on Ebay. I hope it resolves the issue I have spent more than 2,000 on all this engine light P0420 and the shop i took it they messed me up with poor quality of workmanship horrible!

Post by **VStar650CL** » Sun Oct 17, 2021 9:43 pm

The spacers usually work well for killing the MIL from weak cats, but keep in mind that they're also disabling your "early warning system" down the road whenever the replacement cats wear out. That should be a long time, but if the car lives that long, it's something to be aware of.

Post by **jsando2** » Sun Oct 17, 2021 10:03 pm

Yeah! Got ya! I will just put the ones for Bank one which is the one that's giving me that faulty code. I'll make sure I check them Cats once i start hearing or feeling the car all weirded up! I'll come back once i put them on for an update, Thanks!

Post by **VStar650CL** » Mon Oct 18, 2021 4:59 am

It shouldn't be "them", you should only space the rear HO2. Spacers won't work well upstream, especially on cars (like almost all Nissans) with A/F's instead of HO2's on the upstream side. The ECM needs the A/F's to work right. We have a saying that "upstream sensors are for the engine, downstream sensors are for the government." That's because the only real job of a downstream sensor is emissions, monitoring the health of the cat. On the other hand, the A/F's are used directly by the ECM to regulate fuel mixture. So if your O2 is messed up, space it, but if your A/F is messed up, fix it.

Post by **jsando2** » Mon Oct 18, 2021 5:08 am

Thanks but that’s the thing right now I don’t know which one is messed up so I will put the spacer on the downstream and if it still giving me the code then I will know for sure is the upstream

Post by **VStar650CL** » Mon Oct 18, 2021 5:37 am

jsando2 wrote: ↑
Mon Oct 18, 2021 5:08 am
Thanks but that’s the thing right now I don’t know which one is messed up so I will put the spacer on the downstream and if it still giving me the code then I will know for sure is the upstream

That's the right plan.

Post by **jsando2** » Mon Oct 18, 2021 10:17 pm

Well today I got the P0420 on bank 2 as well something new it never happened before just bank 1. Well I hope those extenders fix the issue otherwise I will have to buy those A/F expensive sensors
Will see how it goes.

Post by **VStar650CL** » Tue Oct 19, 2021 4:58 am

Like I said, efficiency codes are common with cheap aftermarket cats. Try the spacers on both banks, chances are that's the whole problem.

Post by **jsando2** » Tue Oct 19, 2021 5:21 am

I will try that first but I was looking a the upstream sensor and I got the wrong one for bank 2 installed

Post by **VStar650CL** » Tue Oct 19, 2021 5:25 am

Well, wrong parts will pretty much always cause issues. Better switch it out.

Post by **jsando2** » Tue Oct 26, 2021 7:42 pm

So today I went underneath to check my O2 sensors and install the O2 Spacers. Well first the spacers are too long I need the short ones and theres not much space to work around. Also I noticed that the Catalytic converter on the lower side theres a gab and I dont see a gasket either, I tried to adjust them but I broke one bolt but it can be replaced no biggie. Im thinking that theres my problem that gap. Well i just bought short O2 sensor spacers and I will take it tomorrow to the shop to see if they can fix that lower side and tighten it up really good. Will see.

Post by **VStar650CL** » Wed Oct 27, 2021 7:53 am

jsando2 wrote: ↑
Tue Oct 26, 2021 7:42 pm
Also I noticed that the Catalytic converter on the lower side theres a gab and I dont see a gasket either

That's very likely. Even a tiny putt-putt exhaust leak at the converter can cause a P0420.

Post by **jsando2** » Wed Oct 27, 2021 8:00 am

I don’t see a gasket there, so you know what type of gasket goes there, I’ve been looking around but nothing let me know if you know which gasket is suppose to be there

Post by **VStar650CL** » Wed Oct 27, 2021 9:53 am

They almost all use crush rings.

Post by **VStar650CL** » Wed Oct 27, 2021 10:31 am

Just confirmed it, should be a crush ring on each one. P/n looks to be 20691-51E01, same on both cats.

Post by **jsando2** » Wed Oct 27, 2021 12:32 pm

Ok so took it to the shop and yes it is the metal oring gasket. They took care of my leak but they said they can’t put the o2 sensor extension because there’s no space for it. I reset the engine light and so far so good and it feels way better let me cross my fingers I hope it stays like that but I’m not too sure about that oh well next will be to buy another catalytic converter but a good one

Post by **VStar650CL** » Wed Oct 27, 2021 12:56 pm

They sell right-angle spacers, in my experience that's what most Nissans need. There isn't usually a whole lot of room between the O2's and the floor of the car. That's what's on my '04 Altie, and you probably need the same thing.

Post by **jsando2** » Thu Oct 28, 2021 6:28 pm

Well tonight guess who came to visit! Yup Mr. P0420. It’s so frustrating aferre spending so much money I’m still in square one. I will try those L spacers to see if it works. My cars are under a spell I’m telling you.

Post by **VStar650CL** » Thu Oct 28, 2021 7:49 pm

You might want to check out this thread if the spacer doesn't work, it has some good pics and a lot of detail I didn't go into here. You might have a wiring issue just like he seems to have, and some scanner work may help you identify it:

topic629985.html

Post by **jsando2** » Thu Oct 28, 2021 9:28 pm

Thanks! he got that same issue still it never says how it ends, anyway i will go with the angle spacers and see how it goes.

Post by **VStar650CL** » Fri Oct 29, 2021 4:18 am

He's still working on it like you are, follow on.

Post by **jsando2** » Fri Oct 29, 2021 4:47 am

Yeah I will try the spacers then I guess it will be a new and better catalyst because with my obd won’t tell me if is a sensor which one is or I just don’t know how to read it

Post by **VStar650CL** » Fri Oct 29, 2021 5:10 am

The spacers usually work, but if they don't, it might be a better idea for you to get or borrow a better scanner. The choppy waveform that @Dedpul's scanner pulled up is what's pointing to a ground issue, and without the scan he could have thrown parts at the problem for months without solving anything.

Post by **VStar650CL** » Fri Oct 29, 2021 5:16 am

By the way, Torque Pro is $4.95 in the Google Store and even a good ELM327 adaptor costs around $18. China-cheap ones are more like $8. So it doesn't cost a lot to have a good scanner right in your smartphone.

Post by **jsando2** » Fri Oct 29, 2021 7:52 am

So this combination of obd and app is better? Will it tell me for example which sensor is jacked up?

Post by **VStar650CL** » Fri Oct 29, 2021 8:15 am

For an extra $2.49 Torque Pro will do realtime graphic plots similar to the ones in @Dedpul's thread, and it's a lot cheaper than a high-end scanner.

https://play.google.com/store/apps/deta ... n_US&gl=US

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