P0420 coming back after new Cat and o2 sensors (1 Viewer)

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Joined
Mar 26, 2021
Threads
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53
Location
Wilmington, NC
Hey guys, need some help here.

Had my CEL come on and pulled p0420. After some searching here, I replaced all 4 o2 sensors and it came back. Replaced the bank 1 cat with a weld in cat from the muffler shop.

Code came back last night. Am I missing something? Could the universal cat not work properly?
 
I could be wrong, but isn’t P0420 code the passenger/Bank2 cat?
*edit ^nevermind- my code was p0430

I had same code and replaced it with one from Rock Auto and didn’t get the CEL afterwards. I also did replace the O2 sensors as well before the cat which did not fix the light. My cat had fallen apart inside and was rattling before I removed it.

Good luck
 
Adding year, millage, build etc to signture line is helpful.

CAT(s) rarely go bad on their own. The cause needs correcting first, or the code comes back. Few exception are prolonged idling, impact, flood waters depositing muck clogging CAT.

Some say miles driven. But the 1 document, 1 million mile 2UZ, still had factory CATS.
 
Adding year, millage, build etc to signture line is helpful.

CAT(s) rarely go bad on their own. The cause needs correcting first, or the code comes back. Few exception are prolonged idling, impact, flood waters depositing muck clogging CAT.

Some say miles driven. But the 1 document, 1 million mile 2UZ, still had factory CATS.

I agree.. Cats don't just go bad.. there may be other conditions if not for the ones mentioned above that may need addressing to really fix the issue. Check the LT-ST Fuel trims. The may indicate what the conditions of your fuel injectors are. I am sure there is a list of troubleshooting steps you already know to go down the list and check to figure this issue out.
 
Thanks for the responses, y’all. Yeah I probably should have done a lot more research before replacing bank one cat bc after reading for a few hours last night, it appears cats are pretty strong.

Here is some details/trouble shooting.
- 2004 LX w/300k miles
- first time got code Indy shop (not Toyota specific) they said bad cat. Did some research here and replaced both bank 1 o2 sensors with denso.
- code came back so I took it to a muffler shop, said it was the cat as well and they replaced bank 1 with a weld in cat.
- code came back so I replaced all 4 o2 sensors with Denso sensors from amazon.
- code is now back again.

Reading live data from scanner bank 1 sensor 1 is reading between .095 and .820. Bank 2 senor 1 is between .100 and .820.

Bank 1 sensor 2 is between .035 and .055 and bank2 sensor 2 is .195 and .210.

All of those readings are at idle. I have photos of readings/graphs if that helps.

D18083CF-B7AA-4023-8201-A12D32BABFF2.jpeg


7BE65406-E9C6-4C83-8DF9-6F77C4FB258B.jpeg


ED222A3E-9976-4499-BCD4-275C0CC2737D.jpeg


5107852E-59E8-4339-9959-3A9260B4A929.jpeg


3DE3C61F-6121-47AE-8268-BC2BE7E33B2C.jpeg
 
Readings before ECT at 187F (operating temp), aren't very useful.

Get reading (Logs that record moment by moment are best), idling.
And
On HWY cruising on level ground, hold pedal stead.
ECT
IAT
STFT BK 1&2
LTFT BK 1&2
RPM
MPH

Looking for signs of engine running to lean or to rich. Especially BK 1.

Look for exhaust & vacuum Leaks.

Any coolant loss, needs noting and investigating. Inspect every inch of head-gasket.

If all checks out, do a compression test.
 
Readings before ECT at 187F (operating temp), aren't very useful.

Get reading (Logs that record moment by moment are best), idling.
And
On HWY cruising on level ground, hold pedal stead.
ECT
IAT
STFT BK 1&2
LTFT BK 1&2
RPM
MPH

Looking for signs of engine running to lean or to rich. Especially BK 1.

Look for exhaust & vacuum Leaks.

Any coolant loss, needs noting and investigating. Inspect every inch of head-gasket.

If all checks out, do a compression test.

Thank you! You dont realize how little you drive at HW speeds until you need to....I guess thats what living at the beach does.

A couple things to note that I've been thinking about over the weekend:
  • Radiator, rad hoses and thermostat were replaced a few weeks ago. Important to note that this issue was/is happening before and after I replaced the rad.
  • Cooling system was pressure tested after and no leaks present.
  • I have noticed a few times over the last few weeks that it has taken a good 5 seconds to start. I didn't think anything of it but after all of the responses and reading into the long p0420/30 thread...there could be something there....
  • Head gasket looks clean from an untrained eye.
  • I don't see any vacuum leaks or exhaust leaks but will probably take it to a shop to see if htey can do a smoke test to be sure.
This after I replaced the PCV valve, air filter and recleaned the MAF. Disconnected battery prior and reinstalled about an hour later. Let idle for 15 min. One PCV hose was badly cracked. Hoping this is my issue but for some reason I doubt it. Ordered the part and should be here in a few days. (nothing local)

Let me know if this helps or hurts. Keep in mind, I am a novice :)

@2001LC
 
Well...One scary thing to note. First drive after doing the above, the first couple of accelerations made a bit of a scary noise around 2,000 - 2,500 RPM. Sounded like the LX was a diesel. It only did it under load. It did not occur when in park or neutral. The noise seemed to have gone away after about 2-3 min of driving.

Any clue as to what that would be?
 
Thank you! You dont realize how little you drive at HW speeds until you need to....I guess thats what living at the beach does.

A couple things to note that I've been thinking about over the weekend:
  • Radiator, rad hoses and thermostat were replaced a few weeks ago. Important to note that this issue was/is happening before and after I replaced the rad.
  • Cooling system was pressure tested after and no leaks present.
  • I have noticed a few times over the last few weeks that it has taken a good 5 seconds to start. I didn't think anything of it but after all of the responses and reading into the long p0420/30 thread...there could be something there....
  • Head gasket looks clean from an untrained eye.
  • I don't see any vacuum leaks or exhaust leaks but will probably take it to a shop to see if htey can do a smoke test to be sure.
This after I replaced the PCV valve, air filter and recleaned the MAF. Disconnected battery prior and reinstalled about an hour later. Let idle for 15 min. One PCV hose was badly cracked. Hoping this is my issue but for some reason I doubt it. Ordered the part and should be here in a few days. (nothing local)

Let me know if this helps or hurts. Keep in mind, I am a novice :)

@2001LC
You can make yourself a quick and easy smoke machine. I made one and posted it in here somewhere. I'll have to look it up link it back to u.

Oh here is the link to the pics and video of the diy Tupperware smoke machine.

 
Last edited:
the waveform from the first picture looks appropriate. The next pics, not so much. Idle or load doesn't matter.
The two rears look bad. As long as the time detail was the same in the last pics as the first.
Buy one more new one and swap in one side and read that one compared to the other side without the peaks and valleys.
V should be .9 to .0999 in all instances. Maybe you could catch a 1 volt here and there.

Don't know about your very last post.
 
furthermore, nothing is going to matter until the ecu is getting appropriate voltage. Ignore fuel trim (all), MAF air volume, etc.
The way it sounds and runs is going to be heavily dictated by the rear o2 sensor voltages/lambda/AFR in all cases in all 100s.
 
Went for a little drive to get some snap shots. The first set is at idle. The second will be at 50ish mph. I def see that bank2 senor 2 is not like the others. Wouldn’t that cause me to throw p0430 and not 420?

39263D1E-4CF6-47E7-9E1A-3C63B9FCBE32.jpeg


929CDA8E-A6D8-4CBC-B998-B8E5F17ABD63.jpeg


5CBE82F8-AA87-4591-B73D-2D2856E147D6.jpeg
 
lol, those are different now.

b2s2 looks like it should, in the last pic.
b2s2 in the pic above the last pic looks bad.

b2s2 in the third pic from the bottom looks bad.

all those look a little bit odd except the last.

low = lean, voltage wise.

rears sensors should really just fluctuate a tiny bit about .45vdc at steady throttle
fronts a little more so. long term % will take longer to even out than short term.

My testing is like this.
at idle in the driveway, closed loop- closed loop happens fast in 100s.
Each sensor's voltage or lambda , afr has a normal range if all is running well. Watch a video.
for narrow bands like on all 100s in the rear rich should get too .999 this should happen standing on the throttle, either in your driveway at a higher RPM or on the freeway, full throttle watch for a peak on your screen if you can't record.



the other thing I do is throttle lift off you should see a .09xx or .1xx or just .1. This is your lean condition, low = lean in narrow band sensors.

perfect world you're looking for .5 to .7 on the rears in almost all driving conditions except full throttle lift off momentarily then back to idle conditions if you continue coasting down the freeway, or a dyno.

fronts should vary slightly and fluctuate a little more rapidly but behave in the same manner and same voltage ranges for narrown band front sensor equipped 100s.


yes, readings like that on your sensors will get you a 430-420, after two trips and a drive above 30 mph I think. it's two trips though.

yes a continually bad rear functioning sensor will eventually kill a cat faster than a normal one, aftermarket even more so.

If you get wild readings like that every time I would look at the engine. Before that though i would verify front sensors are behaving like I'd expect them to. Small short term numbers, correct voltages closed loop idle and mid throttle, open loop full throttle.

Once satisfied the engine and front of the cats is normal then I'd look to the rear.

there's a whole lot of comentary and a whole lot of posts on mud about cats and sensors and 430-420.
I suggest not reading any of them and finding the best utube videos and maybe a actual book.
I'll go find the best utube ones.
 
youtu.be/5WnM_NsOtd8 part 1, youtu.be/cARQ0jZZ4Qc part 2

scanner danner, youtu.be/oRX2V6_a3dc he may bog you down with info.


youtu.be/-JOyjuBwaBE this guy is very smart. Lots of his videos are great.
 
Btw have you checked out the multitude of videos regarding how to tshoot this issue. There are so many that you need to likely filter them to fully troubleshoot this issue.

Here's one - How To Diagnose A P0420 Catalytic Converter Low Efficiency Code Plus Exhaust Leak Testing - YouTube
M
 
Welp, looks like I have some homework to do. Thank y’all very much for the guidance. I’ll check out the above videos over the next few days and try to wrap my head around the readings.

As a side note, took the LX to softball which was a 22 mile round trip. Made 1 stop which means the car was turned on/off 6 times. No stored or pending codes which is odd given the unusual readings. Also the diesel like sound is completely gone. Not sure if it had something to do with replacing the PCV valve or cleaning the TB.

I’ll report back once I get the codes again. I’ll also go ahead and order some new o2 sensors….again 😂
 
hmm dont order anything..make sure you go through the video's these codes are very common.. but also a pita to troubleshoot your first time doing it. But sometimes you learn by dipping your foot into the fire.. :)

btw the O2 sensors you got were original Denso ones right? cause toyo's are very particular on having Denso O2 sensors. Original Denso O2's.
 

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