Yet another P0420 code

So my 2004 Access Cab 4.7 project truck has the check engine light on. With my code reader plugged in it shows the ubiquitous P0420 code. I just replaced all four of the o2 sensors with new Denso’s that i bought at rock auto. I cleared the codes with the reader, but the code popped back on again about 20 miles later.

I’m trying to figure out the next best course of action to take that isn’t overly expensive. The engine has about 218k miles on it. I assume that it still has the original cats. My truck and exhaust is 100% rust free, so i’m positive i don’t have any pin hole leaked. When i removed the engine a few months ago, i didn’t see any signs of a leaky exhaust manifold gaskets. After i reinstalled the engine, i did install new exhaust gasket doughnuts at all the joints. I’m thinking about temporarily install some o2 sensor elimators in order to help narrow down what needs to be fixed.

Does anyone have recommendations on what i should investigate next with my p0420 code?

 

I would check all the o2 sensor connectors for good connection (bent or loose pins), wiring for any fraying or bare spots, and clear the code again before I did anything else. Also take it on a 30 minute highway drive afterwards so that the ECU can run its checks. PITA I know, but its free troubleshooting.

edit: Does your reader have live data? It's reassuring to see very close values on the o2 sensors.

 

The harness and wires are in excellent condition. I inspected every inch of the engine harness (before i reinstalled it and the engine back into the truck). All the pins very 100% corrosion free and rock solid.

I already had a P0420 code before i replaced all four sensors. I cleared the code again after i installed the new sensors. After that i went for about a 30 mile drive. The code popped up again 20 miles later. I then plugged back in the reader and it’s still the same p0420 code.

It’s a actually my friend’s code reader that i’m borrowing. I don’t think it has the live data?

 

Good on you for inspecting the wiring and pins. Its often overlooked.

I use an

$119 OBDLink MX+ OBD2 Bluetooth Scanner for iPhone, Android, and Windows

obd link mx and the free version of their app OBDlink. Having live data is very nice for troubleshooting, and would help verify that none of the new 02 sensors were defective.

Other than the rare possibility a Denso part was DOA it could actually be a bad or clogged catalytic converter.

 

I'd say you need to see the data from the rear sensors to verify if the cats are working or not.

An android phone and simple obd2 dongle will do this. My $1 elm327 off fleabay from years ago does (now $3'ish). You can get the veepeak(iirc) off the 'zon for about $15 or a nicer one like the obdlink for $100+.

I use the torque app on android. The free will work but the pro version ($5?) is a bit better without adds.

 

I had p0420, p0430 codes on our 04 Highlander. It has 226k on it. I ran two bottles of crc guaranteed to pass fuel treatment last Saturday, I cleared them and it’s been gone since. It’s been driven 400 miles since last Saturday. Worth a shot.

 

2nd for the MX+, I've got it too. Very powerful, good smartphone app.

I'm actually really surprised to hear your outcome. It doesn't fit the typical others have seen, and I'm shocked the truck re-popped the code in a scant 20 miles. I'd expect it to take longer to reach full readiness. Fluke?

I'd clear again. And you can always consider throwing non-foulers in the rear, but I'd really want to see some live data to see what is being read. Do you know any history on it, if it'd had some condition prior that was causing it to run rich or lean for any period of time?

 

Full back story...
The engine and the complete exhaust system is out of my 2000 tundra. For the past few years (while the 2000 truck was still drivable), the check engine light was always on. I never tried hooking up a code reader to it to see what the problem was. Since my brother in law was the previous owner, i’ll contact him to see if he ever tried to fix the code.

Right after i swapped 2000 engine and exhaust into the 2004 truck, there was no codes. About 20 miles later the CEL turned on. I’ve cleared the CEL 4 times so far. So far each time it takes about 20 miles for it to turn back on...and that distance has been the same both before and after i replaced all four o2 sensors. I can only assume that the cats are original and have 218k miles on them.

I did inspect my MAF sensor, and it looks clean to me.

 

I think your cats are toast. But you could try the o2 spacer method. I've also been fighting p0420 and p0430 on my 03 for a long time. I replaced my cats and all four o2 sensors, and that helped for a while. I'm going to replace the cats again under warranty next week and see if that helps. If not, I'll try spacers. Keep us posted, and I'll keep you posted as well.
I've tried that cat cleaner stuff on my original cats and it didn't do anything. I haven't tried it on these two years old aftermarket cats yet. I probably won't, since mine are still under warranty.

 

Was the 04 exhaust bad?

 

What brand cats did you install? I’d prefer to not break the bank by buying oem toyota cats.

 

I can only assume that the 04 cats are bad? There was something drastically wrong with the 04 engine, and it was spewing oil out of the tailpipe. When i removed the cats from the 04 truck, oil was pouring out though the honeycomb. I figured it wouldn’t even be worth my time to try to clean them up and install them for testing purposes.

 

I agree. There's a solid chance PO/BIL probably had an upstread O2 failure previously and ran it that way, because a lot of poor suckers believe "Ah, O2 is just that damn federal big brother emissions crap, I don't need it!" (and couldn't be more wrong), it reading wrong caused the ECM to run a/f poorly for extended periods because it wasn't reading exhaust properly, and the mis-burn clogged the cat.

I always try to remember to ask people coming here with inefficiency codes how long it's been going on, or if they've ever popped an O2 code in the past, but sometimes I forget.

On cats, a few brands have been found to not throw codes. Last list I wrote down was: Magnaflow, Walker, Summit Racing's store brand, and OEM. I wish I'd written down a list of ones that throw codes, b/c there are a couple that do. I want to say someone mentioned "if it's listed as accepted for California use, it likely won't throw codes". Maybe that helps?

 

What ever the muffler shop had on hand. I'll find out when I take the truck in for the new ones this week.

 

I'd be curious to know what brand also. Only because what you're describing, battling with P0420/P0430 is what others who didn't use the brands I just listed always bitch about. But I suspect in a few of those cases, the upstream O2 was their initial (and current) problem, and they tossed a perfectly good cat.

 

I crawled under the truck and couldn't find any identifying attributes to the cats.

 

well, huh....it turns out the borrowed code reader does do real time.

 

I have absolutely no idea what all these numbers actually mean though.

 

Will it do a voltage graph of s2 (post cat) while the engine is running?

 

is this the correct screen you’re talking about?

 

Yep.

Is that after driving (engine & cats hot?) or before?

 

Zero driving. It’s just with about 5 minutes of idling. So the engine and cats are warm, but i wouldn’t say there were up to full operating temperature.

 

If i need a new cat, i’d probably just buy a weld in version. https://www.magnaflow.com/products/...compliant-universal-catalytic-converter-51204


It costs WAY less that the direct fit version. I figure i can weld it into place myself for less than $497... https://www.magnaflow.com/products/...-epa-compliant-direct-fit-catalytic-converter


Magnaflow does have some sort of buy back recycling program for your old cat. It’s a “maximum“ of $75 for an OEM cat. The only thing is that they’re a bit vague on just how how much of a rebate that’s you’ll realistically receive. The truck is from california, but is now living in oregon, so i should be find with just installing a federal cat and not a california cat.

 

Get it up to full temp then check the graph again.

The 2nd sensor should be mostly level (minimal voltage swing). If it's not, then the cat isn't doing it's job.

 

Thanks. It’s supposed to be dry tomorrow, so i’ll do that in the afternoon. I still haven’t reinstalled the bed on the back of the truck so i don’t want to be driving around out when it’s raining.

Ironically my buddy text me this afternoon wondering if i was done with using his code reader. I replied that i was not. Maybe my text didn’t go through, because he showed up at my shop about 15 minutes later. He asked me if i was done using it yet. “nope”, i replied. “Good”, he said. “Because my uncle wants me to take a look at his CEL on his car and i’m not motivated to do that today.” So it looks like i got the reader for a few more days!

 

Here’s a pic of after 15 miles of driving. The first pic is when i was driving a steady 55mph on the highway. The second pic is when the engine is at an idle.

 

Looks like the cats may be toasted. My truck is an 05 which has wideband o2 sensors up front but the rears are standard. So newer efi but similar enough.

At 65mph with cruise control on:


At idle just after stopping:

 

“Cats”...as in all both plural of them?

 

Are you also getting p0430? It usually comes something like 50 miles after p0420 if both cats are in question.
P0420 being the driver side and p0430 passenger.

 

Only the p0420 code so far