P0420 CEL code

[Swordsmith]

CEL went on yesterday at some point, didn't notice when it did, maybe on cold start. Turning car off did not clear the code. Checked UG later, code was p0420, which made me think the car might have been smoking something. But I cleared the code and it has not come back so far.

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)

Says here this code comes up when the two O2 sensors are too similar.

I've been running the same mods and same fuel type for several weeks now with no code, so this was a surprise. I'm not too concerned if it doesn't pop up again, it looks kind of bogus to me... but something to look for.

 

[slitzell]

Interesting..

 

[Eric Smit]

your cat is bad. time for a new one. too much e85. get an updated tune to delete the code.


-Eric Smit

 

[firstorbit84]

Or delete the cat

 

[Eric Smit]

still need a tune update.


-Eric Smit

 

[Swordsmith]

I update the tune every couple minutes, I removed both cats and installed a pollution addition device to generate more smog, I have switched from E85 to the more aggressive M85 so now I have a trail of invisible fire following me whereever I go.. and still teh CEL code refuses to come back on. How can I diagnose a problem if it's intermittent!

 

[Eric Smit]

you can get all snarky all you want, you're not the first person to have it and you won't be the last.


-Eric Smit

 

[rdss]

I update the tune every couple minutes, I removed both cats and installed a pollution addition device to generate more smog, I have switched from E85 to the more aggressive M85 so now I have a trail of invisible fire following me whereever I go.. and still teh CEL code refuses to come back on. How can I diagnose a problem if it's intermittent!

Easy, log the car the whole entire time it's running. Build files 1-100 and just keep going through them as you're driving, or better yet, train a rider in the process and increase your driving safety experience while gathering as much data as possible on your car. When the light pops on mark down the log and send it to BNR/Trifecta to get it reviewed.

 

[sonic hotness]

Ya does sound like the cat is bad or 02 is bad.

 

[HADES20]

I've been meaning to read up and learn the codes :/ maybe that one means its time to race someone

 

[sx sonic]

I'm getting the same code, because of my catless downpipe. The code comes up if the 2nd O2 snesors wave form is similar to the 1st O2 sensor (it should be a flat seldom changeing wave form).

Assuming you haven't added a catless downpipe in atleast 200 mi then it would appear you have a bad catalytic converter.

The 1st time mine came up was after about 200 mi and about 60mi since then. (I clear the code with my UG)

If you sent in a log I see no reason why you would have to wait till the light came on, the problem should be apparent thru the O2sensor CEL or not

 

[pwntbywombat]

You can put a spark plug defouler inline with the second O2 and that will fix your issue with the catless down pipe. When I made my down pipes I used a taller O2 bung and I haven't thrown a code.
Edit: threw a code today. The spacer I used wasn't large enough.

 

[AndrewGS]

My 420 came on about 60 miles after installing the catless downpipe. I noticed a performance loss at the same time that didn't go away after clearing the code. The code popped up again about 20 miles later and I'm just waiting for my updated tune to get things back where they should be.

 

[ol_blue]

I haven't got that code yet, but I also left my 2nd o2 out unplugged and all I get is a o2 heater code(haven't updated for the down pipe yet) on the top primary sensor

 

[jeremiah.wells]

Hmmm wonder if error code 420 having to do with dirty exhaust has any anything to do with cannabis

 

[firstorbit84]

I used to get this code on my Audi A6 4.2 (with 4 O2 sensors). A shop told me it was the O2 sensor, so I tried to replace it myself but it was stuck because the car was 10 yrs old and from up north. I soaked it in penetrating fluid and banged on it but it wouldn't break lose. So, I gave up. However, in the course of banging on it, I must've knocked some soot loose and it started working again and the code went away.

 

[Swordsmith]

Couple tanks later and it hasn't come back up, I'm guessing fluke reading. From what I see, the first sensor varies and the second one stays fairly flat, and you get this warning if the two agree too much. So if the first one spiked low while the second spiked high, the two numbers could have momentarily come too close together and popped warning.

Or Erik could be right and either my stock first cat or my DDM second cat could be blown, I'm just dubious about that theory, particularly since I'm running only 15% gasoline, exactly how hard are those cats really having to work?

 

[ss2000slp]

It would be the first cat since there's no o2 sensor after the second. I have almost never seen this code from a faulty sensor without another code present. 99% of the time it's the cat.

 

[Eric Smit]

Couple tanks later and it hasn't come back up, I'm guessing fluke reading. From what I see, the first sensor varies and the second one stays fairly flat, and you get this warning if the two agree too much. So if the first one spiked low while the second spiked high, the two numbers could have momentarily come too close together and popped warning.

Or Erik could be right and either my stock first cat or my DDM second cat could be blown, I'm just dubious about that theory, particularly since I'm running only 15% gasoline, exactly how hard are those cats really having to work?

even though you're only running 15% gasoline, corn still makes exhaust, it's just not pollutants.


-Eric Smit

 

[barch88]

Bumping an old thread...but I just installed the BNR Header and Downpipe, into my ZZP Testpipe and catback. This code is now showing up. Is the reason because I have no CAT's now, or could it be a possible exhaust leak? I'm worried because BNR did not send me a new maifold gasket and I had to reuse that original one, so maybe it could be an exhaust leak...or it could just be because my catless downpipe. What do you guys think? Aside from my car being loud and buzzy now, it idles good and sounds strong...so I'm doubting an exhaust leak. No "ticking" sound like an exhaust/manifold leak usually sounds like.

thanks.