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replaced upstream sensor but PO420 bank 1 code still fires

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Old 05-23-2012, 05:05 PM   #1
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replaced upstream sensor but PO420 bank 1 code still fires

Replaced the upstream sensor with a brand new denso oem upstream sensor that i purchased from ebay...

check engine light comes on after a few days with the same original check engine code that sparked this in the first place "
PO420, "Catalyst system efficiency below threshold Bank 1" (this is the only code it shows)

wondering if the new sensor could be bad or is there likely a deeper problem and what should i do now to tackle this.
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Old 05-23-2012, 05:17 PM   #2
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most likly the sensor is ok along with your old one. primarly p0420 is the result of a bad cat or a bad seconday 02 sensor. the whole job of the secondary 02 is to moniter that the cat is working so ether the cats not working or the secondary 02 is giving incorrect readings
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Old 05-23-2012, 05:19 PM   #3
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Quote:
Originally Posted by trdsteptaco View Post
most likly the sensor is ok along with your old one. primarly p0420 is the result of a bad cat or a bad seconday 02 sensor. the whole job of the secondary 02 is to moniter that the cat is working so ether the cats not working or the secondary 02 is giving incorrect readings
so do you recommend i get the secondary 02 sensor replaced and see from there?? would both cats be bad or just one?
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Old 05-23-2012, 05:23 PM   #4
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P0420 is most likely a bad cat not a oxygen sensor.you need to check the down stream o2 on a scan tool maybe you will get lucky and its bad but i Doubt it.
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Old 05-23-2012, 05:26 PM   #5
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Quote:
Originally Posted by prerunnerSD View Post
so do you recommend i get the secondary 02 sensor replaced and see from there?? would both cats be bad or just one?
you can try it but i don't like to throw parts at things. do you still have the original cat in it
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Old 05-23-2012, 05:26 PM   #6
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so which cat should i replace. there are two you know... people are never clear on this from what ive seen
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Old 05-23-2012, 05:31 PM   #7
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Quote:
Originally Posted by 0psi View Post
P0420 is most likely a bad cat not a oxygen sensor.you need to check the down stream o2 on a scan tool maybe you will get lucky and its bad but i Doubt it.
i hate to say it but he's right. that is the only way of knowing and it can be a cheap scan tool it needs to be somthing that data logs quick and of course you need to know what to look for
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Old 05-23-2012, 05:34 PM   #8
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Quote:
Originally Posted by trdsteptaco View Post
you can try it but i don't like to throw parts at things. do you still have the original cat in it
no i tossed the original sensor...


when you say replace the cat could you please define your terms. this tacoma has two cats.. front and back so not sure which would is recommended to fix with this code.

thinking of calling the dealer at this point.
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Old 05-23-2012, 05:39 PM   #9
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Quote:
Originally Posted by prerunnerSD View Post
so which cat should i replace. there are two you know... people are never clear on this from what ive seen
now im confused are you sure my 02 3.4 only has one its between the primary 02 and secondary 02
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Old 05-23-2012, 05:39 PM   #10
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If you were closer I could probably help you install the new one. It's easy todo your self get the o2 specific socket and then spray the sensor threads with pb blaster great penetrating lube leave it to soak for a min and attempt taking it off
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Old 05-23-2012, 05:41 PM   #11
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the only cat that can set that code is right before "closer th the engine" the secondary 02 sensor idk maby some have a post cat but if there's no 02 to check it the ecu has no idea is there
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Old 05-23-2012, 05:44 PM   #12
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Quote:
Originally Posted by trdsteptaco View Post
the only cat that can set that code is right before "closer th the engine" the secondary 02 sensor
so it would be the 21sty cat the cat closet to the upstream sensor not the main rear cat right?

speaking of cats.. meow girl
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Old 05-23-2012, 05:48 PM   #13
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Im pretty sure california emissions trucks have two cats.one in the down pipe where they come together and one farther down.
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Old 05-23-2012, 05:54 PM   #14
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Quote:
Originally Posted by prerunnerSD View Post
so it would be the 21sty cat the cat closet to the upstream sensor not the main rear cat right?

speaking of cats.. meow girl
its not so much the primary 02 that we care about for this its the secondary thats important to identify the correct cat it will be the cat in front of the 2nd 02 sensor normaly, in this case it's different because both cats are between the primary and secondary 02 sensors. one of the techs i work with came from toyota I'll get a answer from him
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Old 05-23-2012, 05:56 PM   #15
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Quote:
Originally Posted by 0psi View Post
Im pretty sure california emissions trucks have two cats.one in the down pipe where they come together and one farther down.
that wouldn't suprise me its not unusual i just haven't seen one on the east coast
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Old 05-23-2012, 06:01 PM   #16
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so what is my next course of action... i dont mind doing all this stuff myself.. its fun actually.. should i just replace the other sensor and go from there or replace the 21st cat towards the engine... any experts feel free to call me if u have time to explain the situation 619-630-8251 im jonathan
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Old 05-23-2012, 06:03 PM   #17
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massachusetts used cali emissions 2002 so thats could be why it ended up on the east coast.
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Old 05-23-2012, 06:09 PM   #18
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When i put the 3.4 in my 92 4runner i used a o2 simulator i have a cat but the sim was cheaper the the sensor.6 years and no code.just a thought
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Old 05-23-2012, 06:20 PM   #19
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I have been reading about your trouble and I offer this to help. You may want to look at your catalytic converter while it is cold. Look to see if the outer casing is discolored and looks overheated. Look for dents or holes in the casing. Take a rubber mallet or your palm of your hand and strike the converter and see if it rattles, the inner converter material could be broke up inside the casing. If none of that pans out, you may need to remove the converter and look at it to see if it melted in the inside. Good Luck.
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Old 05-24-2012, 05:01 AM   #20
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i just talked to the ex toyota tech i work with he said its the front cat you just need to make sure the rear cat isn't melted at all by looking through it. this makes cents being i front that one will be doing most the work
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