P0420. Bad O2 sensor?

[BadReligion]

Just took the 100 (2003 LX 470) on a 1200 mi road trip and it started throwing the P0420 code (bank 1 catalyst insufficiency). Code would come on and then go off after driving for 30-40 miles. Had a OBD II scanner so I did reset it a few times and it would stay off for a few hundred miles. Really hoping its just an O2 sensor and not the cat. Truck has 126,000 mi. Turned to the live data feed on the scanner and selected all 4 O2 sensors. Both pre-cat sensors had similar readings, fluctuating rapidly between .2 and .9 volts, while the post-cat sensors where a little different. Bank 2 sensor had small but steady incremental changes (looked like steps on the graph) that were dependent on % throttle, while the bank 1 sensor was all over the place. I'm thinking this sensor is bad. Should I replace both sensors on bank 1? Both post cat sensors? Or all 4 just to be safe?

On a side note, this was my first long distance trip in the 100. Really impressed. Cruised all day long at 90mph on the freeway, and was super smooth off road (did 300 miles on dirt roads across Nevada). Nothing too crazy, but definitely some rough NV backcountry driving in the middle of nowhere. When I got home took my 80 to the store and forgot how rough it was, even on pavement!

 

[dynamohm]

Most of the toyota cats I sell have gone bad after long highway trips the PO420 code is for catyalist efficiancy below threshold. most likly it's the cat. Sometimes it's the sensor your readings point to it but a bad cat will also throw the readings off. Using a tech stream would help, will ask one of my techs tomorrow

 

[BadReligion]

Most of the toyota cats I sell have gone bad after long highway trips the PO420 code is for catyalist efficiancy below threshold. most likly it's the cat. Sometimes it's the sensor your readings point to it but a bad cat will also throw the readings off. Using a tech stream would help, will ask one of my techs tomorrow

Thanks! Let me know what he/she says. I always thought it was city driving that killed cats...they couldnt get to a sufficient operating temp to burn off any impurities. I'm still hoping for a bad O2 sensor. If the cat was bad, then I would almost expect the bank 1, sensor 2 to behave like the bank 2 sensor, just at a different voltage. The NOx (or whatever the post cat sensor measures) shouldnt rapidly fluctuate with a constant % throttle.

 

[mgoblue]

I've had the same code after installing my EMS midpipes/exhaust, I also thought I had a bad cat, but it looks like my driver side O2 sensor didn't survive the swap, I'm replacing the O2 tomorrow.

 

[marshotel]

Information in the original post would suggest that the post-cat oxygen sensor on bank 1 only needs to be replaced.

Sometimes it's the sensor your readings point to it but a bad cat will also throw the readings off.

True, but I would certainly just replace that one sensor first and see if it gets rid of the code-

I'd much rather pay for a $70 O2 sensor than a $1200 catalytic converter.

 

[dynamohm]

Information in the original post would suggest that the post-cat oxygen sensor on bank 1 only needs to be replaced.



True, but I would certainly just replace that one sensor first and see if it gets rid of the code-

I'd much rather pay for a $70 O2 sensor than a $1200 catalytic converter.

My tech says it"s the cat a weak one will get overheated on long trips that it what is giving the o2 sensor those readings. If it only costs you $70.00 for a sensor try that first but he thinks it's the cat.

 

[BadReligion]

Just posting an update on this. Kept resetting the CEL with a scangauge and it would stay off for months at a time, then on occasion pop up. Sometimes it would self clear after a few miles, other times I would have to clear the code. Finally, this last month it started coming on more frequently and with winter approaching (throwing a P0420 also disables traction control) I thought I better do something. Ordered up a denso O2 sensor for $40 (bank 1 post cat sensor) and will install it this week. Hopefully that does the trick but I'm not too optimistic. As for replacing the cat, there aren't many options out there. EMS is out of business, DT doesn't make midpipes, and OEM is just too damn $$. I spoke with Slee and they said they have had good experience with magnaflow, who makes a direct fit replacement cat for $500 so if the O2 sensor doesn't work this might be the final solution.

 

[studawg]

What octane fuel have you been running? This article has a paragraph taking about how premium fuel is better for cats.

 

[BadReligion]

What octane fuel have you been running? This article has a paragraph taking about how premium fuel is better for cats.

Just standard 87 octane. Only the M3 and 80 get the good stuff. Its been about a month since swapping out the O2 sensor (10 min install) and so far no P0420. I think this did it! Now when I hook up the scangauge and run a live data feed both the bank 1 and 2 post cat sensors have similar #s, which should indicate there is nothing wrong with the bank 1 cat.

 

[wtmtnterror]

Bumping this to see what the final outcome was. I'm getting same intermittent code P0430, showing up as bank 2, 160k miles. I clear it and it comes back usually within 100 miles or less. Performance doesn't seem to be affected. I saw a Youtube video that someone had posted where a guy was cleaning 02 sensors by heating with a torch, has anyone tried this?

added link

 

[BadReligion]

Bumping this to see what the final outcome was. I'm getting same intermittent code P0430, showing up as bank 2, 160k miles. I clear it and it comes back usually within 100 miles or less. Performance doesn't seem to be affected. I saw a Youtube video that someone had posted where a guy was cleaning 02 sensors by heating with a torch, has anyone tried this?

[/MEDIA]

Still P0420 free after ~9k miles. Skip the torch and order a denso sensor on amazon for $40. I used a live stream OBDII scanner to narrow down the bad sensor the the bank 1 post cat sensor. If you are unsure which sensor is acting up, it might not be a bad idea to get the upstream sensor as well.

 

[greenrover]

Mine throws the P0420 code at the same time every day here in Colorado

 

[BadReligion]

Mine throws the P0420 code at the same time every day here in Colorado

Try some new O2 sensors. OEM catalytic converters are supposed to be good for like 200k+ miles. Unless you ran some real s***ty gas or some weird fuel additive its probably just the sensors.

edit.....just now got that. Damn "rocky mountain high"

 

[TurbineTester]

Good Afternoon,
BadReligion have you had any more P0420 our related error codes since you replaced the bank 1 O2 sensor?

 

[looking4lc]

I have p0430 code. Cleared using obdII. Waiting for my Denso o2 sensor.

Can someone confirm:
Bank 2 is the passenger side in the engine bay?

 

[TurbineTester]

I have p0430 code. Cleared using obdII. Waiting for my Denso o2 sensor.

Can someone confirm:
Bank 2 is the passenger side in the engine bay?

Can you tell me what the DENSO part number is for the pre and post cat sensors? 4260 and 4209 are the part numbers I keep seeing but I don't know which one is upstream and which one is downstream, and are they identical in on both sides?

 

[cwininger]

^this should help you

 

[tzyz]

Hey, just wanted to chime in. I have an 05 LX and lately the check engine light came on but it would go away and then come back so I did some research and it pointed to the gas cap. Kind of made sense so I got a new gas cap and the damn check engine light came back so I bought a code reader and it came back with P0420. I did more research and everyone pointed towards a bad cat or 02 sensor. Seeing how an 02 sensor is about $55 it made perfect sense to try that first. I replaced the downstream 02 sensor and have so far driver about 200 miles and all is good. Interesting part is that my original o2 sensor did not have any nuts on it, not sure how it stayed on all this time. At least it was easy to get it off, one hammer hit. Also, the part number on the o2 sensor I could not find but I went with Denso 234-4154 which was referenced a lot on ih8mud. Anyway, just wanted to let you guys know that changing the downstream 02 sensor fixed my p0420 issue

 

[tzyz]

Hey, just wanted to chime in. I have an 05 LX and lately the check engine light came on but it would go away and then come back so I did some research and it pointed to the gas cap. Kind of made sense so I got a new gas cap and the damn check engine light came back so I bought a code reader and it came back with P0420. I did more research and everyone pointed towards a bad cat or 02 sensor. Seeing how an 02 sensor is about $55 it made perfect sense to try that first. I replaced the downstream 02 sensor and have so far driver about 200 miles and all is good. Interesting part is that my original o2 sensor did not have any nuts on it, not sure how it stayed on all this time. At least it was easy to get it off, one hammer hit. Also, the part number on the o2 sensor I could not find but I went with Denso 234-4154 which was referenced a lot on ih8mud. Anyway, just wanted to let you guys know that changing the downstream 02 sensor fixed my p0420 issue

View attachment 2597513

Also had to buy new nuts to secure the o2 sensor and those nuts are 8m 1.25