P0420

BC

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#1
Make
Toyota
Model
Tundra
Year
2003
Miles
315K
Engine
4.7
P0420 Catalyst System Efficiency Below Threshold Bank 1.

So with this code coming on intermittently, I thinking the catalytic is probably getting old and tired like me! Truck has 315K on it with regular maintenance including tune-ups.

These are very expensive to replace so what if... Or could I... replace with straight pipe and then somehow reprogram the ecm to keep the code from appearing? Or is this a loss cause? Trying to figure out a way around replacing them of course.

Thanks
 

kev2

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#2
unlikely it will work -
AND it is illegal .

suggest you trouble shoot cat code- often another issue causes the intermittent codes.
A look at precat o2 sensor- fuel trims, etc....
 

BC

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#4
Ok, 10-4 on the legalities.

The O2 sensors are all fairly new. Whats the method of checking the fuel trims out?
Thanks
 

nickb2

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#5
replace with straight pipe and then somehow reprogram the ecm to keep the code from appearing? Or is this a loss cause? Trying to figure out a way around replacing them of course.
This would be very difficult. Reprogramming the algorythm for a straight pipe, no. But you can install a cheater.

Yes it is illegal but you don't need to remove the cat, cuz that will cause you problems at time of inspection. This is a viable solution I used back when I was living in ontario. There they have mandatory testing, up here, we simply just don't care.

To fool a PCM, you need access to mode 6, coding skills etc. For a few $ this is way more viable and prone to actually work. It has worked for me many times in the past.

But to cheat, it is quite simple, all you need is a few soldering skills. Some resistors, a capacitor and presto. So just remove the offending cat, use a broom handle or whatever, reinstall and cheat the PCM with this video that should exlain what I am trying to say.

I may get grief from collegues here, but really, one more polluting car in the PPM dept is not going to change sweet f all while our countries devastate forests pass laws that prevent going full electric from lobbying aristocrats.


.
 

nickb2

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#7
On my own personal car, my check engine light has been on since I bought it, scanned it, p0420, and I don't care, have not seen any performance issues.

Although I did use an old tech trick, I fueled with diesel in small shots. My cat got hot enough, it got so hot, it burned off all impurities causing that pesky code. The code went away for a full two months. Came back last week, same code, time to fuel some diesel in my rice burner echo. ;)

Men in my trade have many tricks. Just want to knopw how far you want to go. Cuz I bought my rice burner for 200$. No way in hell I am going to spend $$ on a cat that I can put on my futur 335 beemer twin turbo project.
 

nickb2

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#8
Fuels trims are quite easy. Anything over + or - 10% is suspect.

For a p0420, fuel trims are not important. They will always be out of whack. So either you cheat, then use trims to fine tune the rest, but you can't do that with a bad cat. Hope that answers this question.
Whats the method of checking the fuel trims out?
 

BC

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#9
Ah thats what I'm looking for...Thanks! Yeah we don't have inspections here in FL so I don't have to worry about this part. And I totally AGREE with you on the emissions. I just wonder what one diesel truck is equivalent to in the smog world compared to how many of vehicles like mine? Or one of the so called emission friendly TDI Volkswagen? Believe me... I don't feel bad. If they are so worried about this then why not have a Gov program to reduce the cost of these very expensive cats? I'll find something else to spend my $$ on. Thanks!!
 

BC

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#11
Damn, wish I was there drinking with you all! Thanks nickb2 & Kev for sticking your neck out to show me this info. I'll try this out and report back as suggested.
This will be a good solution for my off road Tundra farm use only vehicle :)
Thanks!!
 
Last edited:

BC

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#13
Problem fixed!
What I did was ordered a scan tool (for android device) from amazon for around $28.00 and then downloaded the turbo app for $4.95. Once the vehicle was warmed up and O2 sensors were in closed loop I noticed my LTFT’s on bank one was -3% and bank 2 was -6% (rich cond.). Upstream O2 sensors were switching back and forth normally. DownstreamO2 sensors bank 1 (problem area) was almost mimicking the upstreamO2sensor and bank 2 was running normally. I waited for another 5-10 minutes to see if anything would change as the truck warmed up even hotter and it did not so I decided to go for a short ride. I ran the vehicle hard for about 5 minutes, pulled over, and rechecked O2 sensors. Bank 1 sensor 2 was now running normally and pretty close to bank 2 sensor 2, nice and flat looking line. My thoughts were at this point, bank 2 sensor 2 was slow acting and not heating up fast enough. I then drove back home, parked and left the truck at idle. I watched the sensors for about 20 minutes more and noticed when the truck cooled off a bit bank 1 sensor 2 was running erratic again. I was contemplating on adding propane to the intake to perform further testing of the response time from rich to lean test on the O2 sensors, but decided to check upstream of the sensors for possible air leaks. What I noticed was on the downstream sensors I had a mismatch and bank 2 sensor 2 was a Bosch whereas bank 1 sensor 2 was the original Denso. Even though bank 2 was not my issue, I didn’t like seeing the Bosch sensor in there as I understand they can be finicky with Toyotas. Makes perfect sense to me… German product should be in a German vehicle right? I decided to change both bank 1 & 2 downstream sensors to Denso. This sensor also could have had some effect on my LTFT as bank 2 was running on the rich side. After installation, in closed loop and all warmed up, the O2 sensors were performing nominally and I also noticed my LTFT’s changed to 0% & 1.8% lean which is well within the normal range. I included a few screen shots of the data before and after. With 315K miles on the truck I’d say the trims look good, but that’s my opinion. I’ve been driving the vehicle around now for over two weeks and P0420 is long gone! I appreciate everyone’s suggestions and thanks nick for suggesting fuel trims as I learned a few good things here. This is all valuable info here on this site! Thank you!!!
 

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grcauto

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#14
unlikely it will work -
AND it is illegal .

suggest you trouble shoot cat code- often another issue causes the intermittent codes.
A look at precat o2 sensor- fuel trims, etc....
I like Kev's suggestion. I think Cats usually fail completely, not intermittently.
When the cat first starts to degrade they will fail and turn on the light and after clearing the code it may take several times for the monitor to fail again and turn it back on. The times between good and bad become shorter and shorter until it'll code everytime. It's always a good idea to check the wiring to the O2 but scopes or graphing with a scan tool can give you good idea if wire chasing is more like chasing your tail.
 

grcauto

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#15
Problem fixed!
What I did was ordered a scan tool (for android device) from amazon for around $28.00 and then downloaded the turbo app for $4.95. Once the vehicle was warmed up and O2 sensors were in closed loop I noticed my LTFT’s on bank one was -3% and bank 2 was -6% (rich cond.). Upstream O2 sensors were switching back and forth normally. DownstreamO2 sensors bank 1 (problem area) was almost mimicking the upstreamO2sensor and bank 2 was running normally. I waited for another 5-10 minutes to see if anything would change as the truck warmed up even hotter and it did not so I decided to go for a short ride. I ran the vehicle hard for about 5 minutes, pulled over, and rechecked O2 sensors. Bank 1 sensor 2 was now running normally and pretty close to bank 2 sensor 2, nice and flat looking line. My thoughts were at this point, bank 2 sensor 2 was slow acting and not heating up fast enough. I then drove back home, parked and left the truck at idle. I watched the sensors for about 20 minutes more and noticed when the truck cooled off a bit bank 1 sensor 2 was running erratic again. I was contemplating on adding propane to the intake to perform further testing of the response time from rich to lean test on the O2 sensors, but decided to check upstream of the sensors for possible air leaks. What I noticed was on the downstream sensors I had a mismatch and bank 2 sensor 2 was a Bosch whereas bank 1 sensor 2 was the original Denso. Even though bank 2 was not my issue, I didn’t like seeing the Bosch sensor in there as I understand they can be finicky with Toyotas. Makes perfect sense to me… German product should be in a German vehicle right? I decided to change both bank 1 & 2 downstream sensors to Denso. This sensor also could have had some effect on my LTFT as bank 2 was running on the rich side. After installation, in closed loop and all warmed up, the O2 sensors were performing nominally and I also noticed my LTFT’s changed to 0% & 1.8% lean which is well within the normal range. I included a few screen shots of the data before and after. With 315K miles on the truck I’d say the trims look good, but that’s my opinion. I’ve been driving the vehicle around now for over two weeks and P0420 is long gone! I appreciate everyone’s suggestions and thanks nick for suggesting fuel trims as I learned a few good things here. This is all valuable info here on this site! Thank you!!!
This is a good way to test these and you are correct about using OEM sensors. There's a quicker way to do this if that scanner has special tests available. You can go into special tests and have it run the monitor while watching the O2's. When in normal operation the rear O2 will read in the .7v area. When running the monitor the PCM will force the engine into a lean condition. You will see the front O2's go to near .1v and as you watch the rear they should come down to the lean as well. The PCM is seeing if the cats are storing O2 and will go from the lean mix to normal and see how long the rears take to react. If they don't stay low for X amount of time it's flagged. If it fails again it'll turn on the CEL. It's a good way to test them but it's not foolproof. If the rears heaters are borderline bad they may cause the monitor to fail. Anytime I see a failed test using the scanner special test I always current test the heater circuit for the offending cat. If it's good then I can condemn the cat if not a new O2 goes in.