P0420 After Valve Cover Gasket Change

Well replacing the downstream sensor did not resolve the 0420 code, back again today. I’ll try to replace the upstream over the weekend and go from there. They could have put it in a little more accessible spot than they did….just gonna have to deal with it.

 

Got the upstream sensor replaced yesterday….what a PIA!!! So far so good but it’s still early.

I did notice that the upstream sensor had a lot more discoloration than the downstream one did…almost to the point that it appeared overheated/cooked??? It’s the one on the left in the picture that I’m attaching.

Regards, Griff.

 

I mean the front one is getting hit by flaming hot exhaust, it should look more cooked. It's not like it's that much cooler at the downstream, but some filtration and dissipation happens between the two.

Drive cycle should complete with mixed driving within 20-50 miles. Each make/model has a different formula it uses to run its tests, some are quick, some are painfully slow. One of my late 90s VWs had the worst, most convoluted drive cycle I've ever seen.

Keep us posted!

 

Generally P0420/0430 means the oxygen sensors are working properly and the post cat sensor is switching with the upstream, indicating degraded catalyst.

Without scan data of all four sensors you couldn't confirm that.

Upstream should switch up and down, downstream should stay steady.

Also, use good sensors (OEM, Denso, NTK)

 

It totally can be that. But that code will also light up if either the upstream or downstream is seeing a slow failure/death, sending slightly askew values to the ECU, which isn't unheard of or uncommon.

It's a hell of a lot cheaper to replace the upstream and downstream sensors (especially if old, consider it proactive maintenance) than it is to replace the cat with one that won't toss codes, which is significantly more expensive. Others have already found out, trying to find a cat for these trucks that won't throw codes is difficult.

Best part is, if it's not a case of one of the sensors being slightly askew because it's on its way out, and you do hafta replace the cat, guess what you won't be spending money on again over the next 10-15 years if you used OEM parts?

Then again, as I mentioned in my 1st reply, you can throw codes like this from having a leak between ignition source and O2. I'd expect to see more than one code in that case, but ...

 

Day 2 of driving since the upstream sensor was replaced with no code thrown. Maybe that was the problem???

 

Fingers crossed it was, I feel like my reputation is on the line at this point

Curious to see week 2 update, week 3 update, etc.

 

Well I’m sad to report that the P0420 code is back…has anyone tried the cat cleaner that you put in your gas tank or is it just a waste of money? Any recommendations on where to purchase a good cat without breaking the bank??

 

What Brand reader is that you posted on page 1 ?




Do you know if it shows live data ? Be great if it shows graph and/or simple voltage readings.
Upstream reading should go from approx .8 vdc(rich)- .1 vdc(lean)....sine wave pattern
Downstream reading should be less than . 45 vdc, approx .2 vdc(lean) but somewhat of a straight line.
Lot of money to spend on a Cat without knowing what the actual readings of the O2 sensors are.

 

Cat cleaner is generally regarded as a waste of money, gimmick. There are all kinds of stories out there about ways you can submerge the cat in fluids, bake it in the oven, it's all BS in my opinion.

As far as cheap, that's tricky. Especially with your V6/4.0L. Folks have thrown codes from using cheap aftermarket.

A lot of luck has been had with MagnaFlow and Summit products. If you have a shop that can weld it in, Magnaflow 51204 is a "universal" weld-in cat.

Likewise, I know at least @N84434 had luck with Walker brand, they have a slip-fit product, either part number WLK-83600 or WLK-83800, the WLK-83600 seems reasonable price, and he hasn't tossed any codes in 2-3 years. @TurdFerguson also ran Walkers for ~4 years, no codes. CHECK FOR CORRECT P/N! (I used Summit Racing to verify), but again, you may want a shop to install.

That's about the best I can do ...

And definitely That too ^^

Although the Walker universals look like they only run ~$300...

 

I can look tomorrow for the brand…purchased it from Autozone, wasn’t that expensive, I believe it just reads codes.

 

Thanks, I’ll start shopping around, I can handle the welding myself.

 

Yes, I bought the Stem to Stern Walker exhaust system and it's been fine for nearly 3 years. I initially painted all the sections with BBQ Black paint, to protect it from rust for as long as possible, and I've touched up the pipes a few times over the last couple years.
So far so good...

 

The saga continues, no check engine light on this morning when I got in it to go to work or on the way home this afternoon. I wish it would makes it mind up on what it wants to do.

 

This may suggest you had more than one problem. i.e. potential leak somewhere exposed aging O2, for example.

I'd roll with it for a while longer, make it through several more drive cycles and keep an eye on it to see if any more codes pop.

Not saying it would hurt to toss a new cat on it. Well, it'll hurt the wallet for sure...

 

That’s exactly what I had in mind. It’s not running bad so just gonna see how it goes for a few days.

 

3 days without a code….83 miles.

 

This is the exact same issue I have on my 4.7 the CEL stays on more than it stays off but every now and then it stays off for a day or two. Which has me thinking I have a leak somewhere or my o2 upstream is bad. FYI the cheapest code reader from Harbor Freight will give you Live data.

@BubbaW would those voltages be the same on a 4.7??

@Griff04 I know you didn’t mess with exhaust in any way but what about exhaust gasket leaks? Or exhaust manifold going bad?? Or checking all those nuts and bolts to make sure nothing is seeping out from that area??

 

I'll help you fish a bit:

2000-2003 FSM and although it doesn't apply to you, but someone else may need it, 2005-2006 FSM

 

Thank you the link isn’t working for me but I do have the Haynes manual I am sure I can find the info in that one??

 

I guess, if you want IKEA instructions versus the Encyclopedia Britannica edition.

I just updated the link. Have fun with what the Toyota technicians use.

Never trust Haynes/Chilton more than the field service manual.

 

I’ve looked several times but couldn’t find anything loose or leaking. If it were some type of exhaust leak I would think that it could be heard. I haven’t given up on it yet.

 

thanks for the link, I’m sure it will come in handy at some point.

 

Be sure to download it and keep in a safe place. A couple of the links posted here have gone dead already.

It's not ideal, it's not the perfect manual, the links in them to quick-jump to sections are broken, but you can utilize the Search feature to find where the links are jumping to.

 

So I got around to looking through the manual…please correct if I’m wrong, from what I’ve read online bank 1 is the driver’s side but in the manual if you look in the Emissions Control-V6 section on page EC-12 the picture calls out bank 1 on the passenger side….am I missing something?

 

You've got the V6, you're probably reading V8 info online.

When searching for info on your engine, search for "1GR-FE" and you'll always get accurate info. The manual is correct, as shown here, and I'd add the firing order is sequential:

​

 

Excuse my language but what a “dumb ass”, I’ve been working on the wrong dang side. Well at least bank #2 has new sensors. I did save the old ones so I might just stick them to see if it clears the code, if it does I’m just going to roll with it.

 

I'd find that really weird if so. I hope this wasn't related to my admitted confusion earlier, thinking you had a V8, since that's the predominant engine everyone's got.

But yeah, you can always swap driver to passenger, and if you didn't throw away the old ones, you could try swapping the old bank 2 pre-cat into bank 1 pre-cat spot and see what happens.

 

Gonna try to swap them on Sunday…I’ll give an update.