P0420 - Replaced A/F after P1130/1135 a few months ago... now P0420 low ?? Bank 1

H

Headly

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Are all P0420 codes the same ? are they all Bank I ???

Does an OBDII scanner say P0420 Bank 1 or P0420 bank II

If the scanner reads Code P0420 Bank 1 low whatever ??- can that still be the rear O2 sensor ?

I replaced my a/f sensor in front of Cat 1 with Denso 234-9002 @ 141k miles about 2-3 months ago.

Previous owner did rear O2 @ 95k - current miles are 143k

P.O. also did @ 130k - MAF,plugs,wires,fuel filter,timing belt,water pump

I will check for exhaust leaks tomorrow, I will get the multi-meter out and check the a/f sensor to see if that pooped already,but that code was a different one than P0420 - those were P1130 & P1135 when the a/f sensor went bad- could it be a ground issue with the O2 sensor ?

Man it is cold outside,but I want to fix this sucka
 
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too much lake effect snow and cold to get under the 4 runner today.. cleared the code,will have to see how long it takes to come back

having a front wheel bearing done tomorrow by garage that installed the Denso 234-9002 to get rid of my CEL for the P1130/1135 codes- gonna have them check the ground and sensor out put

still curious if all P0420 codes read the same bank I or not

I could put a new rear O2 in,or I could try telling company I bought the Denso 234-9002 off of through amazon it is bad already,but if it were bad already wouldn't it throw the same codes as before it was replaced?

coolant level and oil level have remained unchanged - so it appears leaking fluid can so far be eliminated .. so far & hopefully forever lol! =)
 
it's in the shop for the wheel bearing.

if there is no exhaust leak... is it definately the cat ?

rear O2 replaced @ 95k / front O2 a/f sensor replaced a few months ago ?

should I try a new rear O2 or jump into the cat ?

went 20 miles before CEL came back on after resetting it,it was a 1 hor 20 mile drive, actually 2, 1/2 hour- 10 mile drives in the heavy snow and the cel came on again after a heavy puddle - hopefully it is a connection
 
Nelsonmd said:
I disagree, get an aftermarket one and a URD simulator.
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Well that will work too, that's what I have, two eastern cats and the URD sim. But by doing so it doesn't guarantee that you will pass emissions testing (if applicable) for the OP's state. The URD sim basically fools the computer into thinking everything is ok with the O2 sensor, when it may or may not be.

So I guess it just depends on your tolerance to risk, if you have to pass some sort of emissions testing.
 
jsmarine said:
Well that will work too, that's what I have, two eastern cats and the URD sim. But by doing so it doesn't guarantee that you will pass emissions testing (if applicable) for the OP's state. The URD sim basically fools the computer into thinking everything is ok with the O2 sensor, when it may or may not be.

So I guess it just depends on your tolerance to risk, if you have to pass some sort of emissions testing.
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That's true. Does Cali still do emissions tests? I thought most states just went by CEL's instead of doing emissions tests.

It is sad when you can buy the simulator and 3 cats for less than just 1 OEM cat. I will have to go that route when I finally decide to get rid of my 0402 code.
 
P0420 is a fickle code. Reset it, log the mileage, and see if it comes back. I've reset a P0420 a few times now but can't remember the last time it came on. If everything is ok with the sensor and the exhaust, like mine was, I would just reset the code and wait it out.
 
Headly said:
still curious if all P0420 codes read Bank 1 low ..

bump ?
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On our cars, YES. We only have Bank 1 on 3rd gens. You only have a bank 2 on cars with dual exhausts.

Unless you have done it in recent history, changing the rear O2 sensor is worth it. Usually when a front (A/F) sensor goes, the rear is not long for this world. P0420 is most commonly associated with the rear O2, exhaust leaks, and the cats themselves. I would certainly exhaust the first two possibilities before trying the third, or going to a sim.

I also agree with 004Gunner above. Reset and see how long it takes to come back. I had a random p0420 in August, reset it, and have not seen it since. When my rear O2 died three years ago, it would trip every three or four months at first, then it got more frequent until it was tripping every tank. I swapped the rear O2, and then never saw it again except for the random shot in August.
 
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cool - thx for stopping by guys,mucho appreciated in fact

I reset the code by undoing the battery - I drove for 1 hour/20 miles in heavy snowfall/lake effect/traffic standstill before light came on again after driving through a big wet puddle-coincidence ? that is what happend when it came on 1st time,doh!

I have full service history on 4runner from p.o. - he did rear O2 @95k it now has 143k - I did AF sensor/front O2 3-4 months ago(141k)

the exhaust does NOT smell rotten egg at all and it breaths nicely too- oil and coolant levels seem unchanged from last service

I believe I will try rear O2 before I mess with a cat. How much is a rear O2 $100 or less

I wanted to be sure the code Bank I low ... ??? wasn't front only as feared by myself

What I got thinking was how can bank I read front CAT when A/F sensor / O2 on cali emission vehicles from 2000 are BEFORE first cat ..... so if my mileage is still ~17 and it doesn't smell bad,and it seems to flow freely - rear O2 might be a good idea eh?


thx for the input guys - I know the Po420 code has had lots of threads and I do appreciate the feedback -thanks!!!!!!
 
IF ... I do replace a CAT - how bad is Magnaflow- I recognize the brand and they are much much cheaper/more reasonable than toyo

I read ya might get 2 yrs out of a magnaflow cat - that sounds like a good deal to me unless they throw codes,then it aint worth a penny ..
 
well - maybe good news.. stopped by local shop today and asked if I could have the exhaust looked at and yuppers,the doughnut/gasket between a/f sensor front cat and straight pipe is bad- it was closing time so I get it replaced tomorrow- fella said a leak would limit flow to rear cat and throw a code, I sure hope so =))))

BTW - HUGE thanks to the board members for their help whether the ex. leak is the fix or not ,thx!!!!! :frog::frog:
 
Headly said:
well - maybe good news.. stopped by local shop today and asked if I could have the exhaust looked at and yuppers,the doughnut/gasket between a/f sensor front cat and straight pipe is bad- it was closing time so I get it replaced tomorrow- fella said a leak would limit flow to rear cat and throw a code, I sure hope so =))))

BTW - HUGE thanks to the board members for their help whether the ex. leak is the fix or not ,thx!!!!! :frog::frog:
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Oh you lucky bas****o. Exhaust leak is one of the causes of an 0420. You probably just saved yourself some money.

I checked mine for a leak, but couldn't find one. It is so rusty that there may be one, but I sure couldn't see it.

Let us know how it turns out.
 
ex. leak fixed,light reset

only 33 miles so far and no light. last time I reset the light it lit up ~20 miles so hopefully good news

a $50 fix would be awesome- $1/2 hr labor,& ex. gasket
 
Headly said:
ex. leak fixed,light reset

only 33 miles so far and no light. last time I reset the light it lit up ~20 miles so hopefully good news

a $50 fix would be awesome- $1/2 hr labor,& ex. gasket
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Well, the cat test is the last to finish, so it may take a while to finish. I usually go about 120-200 miles before it finishes the check. I think it's also related to the number of starts.

I'm still not going to care about my 0420 that much, at least not until next fall when I have to get it inspected again.

Keep us informed.
 
356 miles - no CEL light nor does it show anything amiss on the scanner - it was the exhaust o-ring between the front cat and straight pipe fwiw

Best of luck with the P0420 codes, may you all have it be just an exhaust leak !
 
Headly said:
356 miles - no CEL light nor does it show anything amiss on the scanner - it was the exhaust o-ring between the front cat and straight pipe fwiw

Best of luck with the P0420 codes, may you all have it be just an exhaust leak !
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Thanks for posting back--too many times we don't hear the end of the story. Glad you got off cheap!
 
TheDurk said:
Thanks for posting back--too many times we don't hear the end of the story. Glad you got off cheap!
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yup - I hate when I go searching for info and after 2 pages it ends w/o an answer..

600+ miles no light

The PO did cat back exhaust @ 90k when he did rear O2 sensor,and I just had a front a/f-O2 sensor Denso installed - when I noticed the truck get a bit louder after the light went on I felt positive about exhaust leak as remedy
 
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