P0420

[2ndhandyotaman]

Yeppers- I took the 'runner for it's longest trip so far, about 45 miles up Interstate 83 from Baltimore to York, PA this morning. It ran as well as it has, nothing out of ordinary then on the way back, I noticed a glowing yellow CEL.

I stopped by a parts store for a free scan and the "expert" diagnosis that always seems to follow along with said "free" service, along with a print out of the part that they stock to fix the issue.

Naturally, I was told that it HAS to be the converter. I asked 'which one' with the reply being a blank stare then the $100,000 answer= "the only one"

I left and started doing me research, apparently this is more of a blanket trouble code- it just tells you that something is wrong, but that's aboot it. I know from talking w/ the previous owner, the A/F sensor was replaced along w/ a new MAF and air box ( due to cracking from age ). Visually I can see the new parts, so this attempt from a Toyota service dept helped for a while. Now I'm holding the bag-o-poo and need to do something about it.

I can see visually that the rear oh-2 sensor looks to be original- the studs that hold it in place are a ball of rusty crud. They aren't coming apart peacefully, more likely in pieces. From all of the threads in these pages on this very code, it seems that the consensus is to replace the rear sensor no matter what, and work forward from there? I have a buddy with decent scanning software, but he's a body shop so his guys can only use it to reset sensors in crashed cars, not trouble shoot running issues. I'm going to attempt to use it tomorrow and see if I can get it to live stream data, looking for voltages at each sensor.

If anyone has had recent success chasing down this issue, please feel free to chime in with any diagnosis procedures. Thanks !

 

[2ndhandyotaman]

Just an update in case this info is helpful to anyone. I borrowed a Actron CP9580A scan tool today and did some live stream data logging. I saw that the upstream sensor never moved much beyond .650 V while the downstream sensor was bouncing all over the place between .375V / .750 V This is exactly opposite of what you would expect to see if the system was functioning properly. Since our emissions management system doesn't use a sensor between the 2 cats, the downstream sensor is seeing an "average" of the work that 2 cats are doing.

From my research, the downstream sensor should stay right around .5V with very little fluctuation, the upstream should be constantly updating and having a lower voltage then the downstream. My readings tell me that the motor is dumping a lot of unburnt fuel into the exhaust stream. Before I spend $$ for new cats, I will check the ignition system to see if I have worn plugs or anything else that could be contributing to the issue. My truck has 200K on it, so it's not out of the question for the cats to be shot, I just want to be sure I'm spending the money where it needs to be spent.

I'll update as I dig deeper into this issue.

 

[TheDurk]

Just an update in case this info is helpful to anyone. I borrowed a Actron CP9580A scan tool today and did some live stream data logging. I saw that the upstream sensor never moved much beyond .650 V while the downstream sensor was bouncing all over the place between .375V / .750 V This is exactly opposite of what you would expect to see if the system was functioning properly. Since our emissions management system doesn't use a sensor between the 2 cats, the downstream sensor is seeing an "average" of the work that 2 cats are doing.

From my research, the downstream sensor should stay right around .5V with very little fluctuation, the upstream should be constantly updating and having a lower voltage then the downstream. My readings tell me that the motor is dumping a lot of unburnt fuel into the exhaust stream. Before I spend $$ for new cats, I will check the ignition system to see if I have worn plugs or anything else that could be contributing to the issue. My truck has 200K on it, so it's not out of the question for the cats to be shot, I just want to be sure I'm spending the money where it needs to be spent.

I'll update as I dig deeper into this issue.

Since you have two cats, then that front sensor is a wideband A/F sensor, and it doesn't work that way. The PID 1) reports only one-fifth of the actual voltage and 2) it is a fixed reference voltage of 3.3V (or 0.660V on your scanner.) It won't bounce around like an o2 sensor does.

Time for a little RTFM:

http://www.teamtoyota4x4.org/archivio/1996%20to%202002%20Toyota%204Runner%20Repair%20and%20Wiring%20Manuals/techinfo.toyota.com/ileaf/02toyrm/02toypdf/02rmsour/2002/024runne/di/eg5vzfe/cip0125o.pdf

 

[2ndhandyotaman]

Thanks for that link, that was the kind of information that I was trying to find and never did. So it would seem that the upstream sensor is indeed working correctly, the minor voltage changes while driving and data streaming showed that condition. Should the downstream sensor then be showing a constant voltage change as it sends signals to the ECU for A/F ratio adjustments?

This was during a drive w/ engine at 2200 RPMs.

 

[2ndhandyotaman]

A bit more diagnosing today and found these- this can't be helping anything especially when #6 plug was only held in by 1 turn of the socket and the plug wire that runs to #5 from the coil wasn't making full contact with the terminal. Evidence of arching and a corroded terminal wasn't helping anything either.

A bit of cleaning up of the coil terminal and a dab of di-electric grease should help out, along with a fresh set of the correct NGK spark bolts. I cleaned up the throttle body while I had it right there as well as cleaned out the PVC and fixed a cracked air hose going from the silencer to somewhere in front of the TB ( it connected to a flared steel line).

The truck started much easier and ran much smoother and quieter. I plugged in the scanner and went up and down the interstate checking the readings and comparing them to the prior readings. The Voltage numbers on the down stream sensor ( O2) didn't fluctuate as much as before and the upstream A/F sensor stayed steady.

Since the link that TheDurk gave me, it completely changed the way that I was interpreting the info. Does anyone else have a screen shot of a similar live data scan that I could compare my info to? I have no idea if/when my P0420 CEL will return, it could be beneficial to have know good data to compare my readings to. I'm hoping that the maintenance today will help the CEL, I'm just not convinced that I've actually fixed the root issue.

 

[19963.4lsr5]

Watching the rear sensor in graph format is more helpful if your scanner has that option.

My 97 repair thread shows some graphing of the rear sensor after my P0420 reared its ugly head again.


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[2ndhandyotaman]

Well, the CEL came back on today. I scanned it and got the P0420 again. ( no surprise ) so the cat cleaner in a can doesn't work worth a poop. I had my doubts but it was worth a try, right? I guess the other way to look at it is- it was $23 that could have gone towards the proper repairs.

What next ?? I'm considering trying anew downstream sensor, although the scan tool shows that the one is working, so that might be another waste of money/effort. I saw the classified ads where someone in Buffalo, NY is scarpping a 3rd gen w/ only 123K on it. I dropped the question about selling his cats, we'll see. In the mean time, I've found Rock Auto to be the least expensive option for new after market parts using Bosal brand ( good stuff. I've used Bosal exhaust products on European cars for decades without any headaches) Locally walker /gorlech-AP is available, I really don't want to use that stuff. It simply doesn't last nearly as long and it isn't much cheaper than the mail order Bosal.

Am I over looking any other diagnostic procedures before I buy new(er) cats ? I've been looking at the youtube vids from Eric The Car Guy , South Main Auto Repair and a few other "credible" YT channels plus I've spoke with a trusted shop that is next to my buddies body shop who informs me that they can predict 100% that after replacing the upstream sensor on a 3rd gen runner/Taco the vehicle will be back within a month with P0420 again and the only course of action left is to replace the cat and NoX scrubber.

I'm not trying to avoid the repair ( except financially- it will put a big strain on me right now) but I just want to be 100% sure that replacing cats will fix the issue. I had no signs of coolant or oil contamination when I changed out the wrong spark plugs last week so I'm feeling OK that the motor isn't contaminating the cats, When ever I've replaced cats in the past it was because of road damage or you could hear the honey comb rattling around, I've never dealt with a cat just dying a natural death.

 

[gamefreakgc]

Well, the CEL came back on today. I scanned it and got the P0420 again. ( no surprise ) so the cat cleaner in a can doesn't work worth a poop. I had my doubts but it was worth a try, right? I guess the other way to look at it is- it was $23 that could have gone towards the proper repairs.

What next ?? I'm considering trying anew downstream sensor, although the scan tool shows that the one is working, so that might be another waste of money/effort. I saw the classified ads where someone in Buffalo, NY is scarpping a 3rd gen w/ only 123K on it. I dropped the question about selling his cats, we'll see. In the mean time, I've found Rock Auto to be the least expensive option for new after market parts using Bosal brand ( good stuff. I've used Bosal exhaust products on European cars for decades without any headaches) Locally walker /gorlech-AP is available, I really don't want to use that stuff. It simply doesn't last nearly as long and it isn't much cheaper than the mail order Bosal.

Am I over looking any other diagnostic procedures before I buy new(er) cats ? I've been looking at the youtube vids from Eric The Car Guy , South Main Auto Repair and a few other "credible" YT channels plus I've spoke with a trusted shop that is next to my buddies body shop who informs me that they can predict 100% that after replacing the upstream sensor on a 3rd gen runner/Taco the vehicle will be back within a month with P0420 again and the only course of action left is to replace the cat and NoX scrubber.

I'm not trying to avoid the repair ( except financially- it will put a big strain on me right now) but I just want to be 100% sure that replacing cats will fix the issue. I had no signs of coolant or oil contamination when I changed out the wrong spark plugs last week so I'm feeling OK that the motor isn't contaminating the cats, When ever I've replaced cats in the past it was because of road damage or you could hear the honey comb rattling around, I've never dealt with a cat just dying a natural death.

On previous Toyotas that use similar sensors, they actually were a regular maintenance item every 90k miles to ensure proper function. That's not the case anymore but they still have a limited life being blasted by insanely hot exhaust gases.

Amazon tends to have the correct DENSO sensors for the cheapest. Just make sure you get the right part number, you can look it up on DENSO's North America site. Will depend if it's 2WD or 4WD, 1 or 2 cats, etc. Replace the sensor and go from there.

If your exhaust smells like rotten eggs & skunk spray all the time, then your cats really are failing.

 

[TheDurk]

I would recommend changing the rear O2 if has not been done, before I bought new cats if there is no apparent physical damage. The ECU tests are not good enough to detect a working sensor that has degraded just enough to trigger a P0420. I cured a stand-alone Po420 three years ago with a new rear sensor and so have lots of other people. And, in any case, if you put new cats, you want new sensors, front AND back, to go with them so you are going to spend that money anyway.

 

[2ndhandyotaman]

Thanks for the feedbacks, opinions are always a good thing. FWIW, I do not have any "stinky" cats. I need to hit them with a IR gun to check temps for a quick temp check to see how they're functioning, but I do agree that a new rear sensor wouldn't be a bad idea because if I go to new cats, I'd want the new sensor anyway. The upstream sensor was replaced at a dealership about 1 year/10K miles ago along with the MAF and the air box.

 

[19963.4lsr5]

My 420 returned after 4000 miles tooling along in traffic. In the snow......

A new O2 sensor didn't clear the code by itself.

I messed around with the cap and resistor mod to see if I could get the code to go away on its own. But no.

So I reset the code since I had to pull the battery and installed the new rear O2 to see how long it stays away. Hopefully it's as long as Durk.



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[2ndhandyotaman]

^ I was looking at your thread, you had one heck of a project bringing that 'runner back to life. As much I can appreciate a good 'work around' to make a problem go away, I'm going to keep plugging away at this issue until I figure out exactly what the issue is and fix it once and for all. ( at least for the time being...)

I was able to figure out that my 'runner has California emissions ( 50 state vehicle) so there's only 1 Denso O2 sensor- 234-4153 Amazon has them for under $50 shipped 3 day mail. Good enough for me. I'm mad at myself for wasting $23 on the can of snake oil, lol.

The nuts holding in the Oxy sensor are just a ball of rust-crud. I'm expecting to have to drop the pipe and drill/tap the studs for new hardware. Fun times..

 

[Robb235]

Spray a healthy amount of PB Blaster on the rusted studs and nuts, and let sit for several minutes.

I've had the P0420 code, and replacing both O2 sensors didn't fix my issue, nor did cleaning my MAF. Doing the capacitor and resistor mod turned off the CEL for me.


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[19963.4lsr5]

In my case I think in slower traffic my CAT is cooling off and shutting down. I haven't checked the crossover pipe and cat bolts for air leaks. But my rig is getting good milage this time of year. And if I'd have a leak before the pre-cat O2 sensor I'd expect LTFT to be skued to richen up the mixture and my mpg would be lower than normal. Normal for me is 18mpg.

Above 2000rpm it seems to operate correctly. And in doing that, the Cap and Resistor dropped the signal to the ECM too much. Making it out of range.


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[2ndhandyotaman]

That's one thing that I noticed about this '99 compared to the '01 that I sold- the '99 gets worse mileage. I'm averaging 16 MPG in mixed driving, not very much long interstate driving yet.

I was ordering the downstream sensor last night from Amazon when I noticed that they were going to charge me 6% state tax on the purchase. I said 'screw this' and got it from Rock Auto for literally .50 more. Something about paying a state sales tax on an item that isn't coming from the Baltimore warehouse just rubs me the wrong way, so RA got the sale instead.

As for rust, I have the best formula ever to be mixed up- ATF and acetone, 50/50 solution. I've taken apart hardware that I would swear was just going to crumble when breathed on. That being said, I'm pretty sure that the hardware holding on the sensor is just going to crumble, it's really that bad.

The part will be here in a few days, I'll update the progress next week.

 

[TheDurk]

That's one thing that I noticed about this '99 compared to the '01 that I sold- the '99 gets worse mileage. I'm averaging 16 MPG in mixed driving, not very much long interstate driving yet.

I was ordering the downstream sensor last night from Amazon when I noticed that they were going to charge me 6% state tax on the purchase. I said 'screw this' and got it from Rock Auto for literally .50 more. Something about paying a state sales tax on an item that isn't coming from the Baltimore warehouse just rubs me the wrong way, so RA got the sale instead.

As for rust, I have the best formula ever to be mixed up- ATF and acetone, 50/50 solution. I've taken apart hardware that I would swear was just going to crumble when breathed on. That being said, I'm pretty sure that the hardware holding on the sensor is just going to crumble, it's really that bad.

The part will be here in a few days, I'll update the progress next week.

You MAY find that the nut crumbles to dust, but the stud can be recovered with a stiff wire brush and maybe a thread chaser. The studs are made of much harder stuff.

 

[a216vcti]

You MAY find that the nut crumbles to dust, but the stud can be recovered with a stiff wire brush and maybe a thread chaser. The studs are made of much harder stuff.

I experienced this as well.

OP, what's your long term fuel trim reading?

 

[2ndhandyotaman]

I don't remember off hand, I'll get a new reading and post the info. On a positive side note- I ordered the part on Thursday night- it was waiting for me when I got home tonight. I just used standard shipping and was expecting it on Thursday. Looks like I'll tackle this tomorrow and get it done

 

[19963.4lsr5]

I don't remember off hand, I'll get a new reading and post the info. On a positive side note- I ordered the part on Thursday night- it was waiting for me when I got home tonight. I just used standard shipping and was expecting it on Thursday. Looks like I'll tackle this tomorrow and get it done

My friend worked at the local Toyota dealership for a while and said they dealt with the rusted to nothing nuts by removing the studs and using short stainless bolts.


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[2ndhandyotaman]

I experienced this as well.

OP, what's your long term fuel trim reading?

This is what I got today. I wussed out on installing the new sensor, I didn't get started in time to beat the weather. It looks like a 'go' for tomorrow so hopefully I can get it done.

No impending codes yet but I wouldn't blink an eye if the light triggers tomorrow as I drive around the beltway to get to my storage unit where I sneak in some work while trying not to get caught by the property manager.