01 Tundra P0420 code

Hey all so I just got this code earlier tonight. I did some research and apparently it seems that the truck just needs some simple maintenance (check the engine air filter, MAF sensor, possible throttle body). In the past usually the P0420 code means that the O2 sensor is bad, but based on the videos that I've seen, its either replace the bank 1 cat converter or clean the engine compartment. Can someone possibly clarify on this please? Now I honestly don't know the status of the current cat, but overall the truck has been running fine until tonight. Besides, I was planning on doing a general cleaning anyways at the beginning of the year, but maybe it sounds like it needs it now?

 

See this:

• Cat inefficiency codes P0420 and P0430: Strong chance it's not your cats. Read why HERE.

Taken from this thread: https://www.tundras.com/threads/so-you-wanna-buy-just-bought-a-1st-gen-tundra-eh.115928/

You can go watch videos all you want, and they can tell you generic ass reasons about what that code means with hundreds of other models of trucks. It's virtually NEVER the cats with our trucks. It's either the upstream air/fuel sensors are bad, some dumbass prior didn't know these trucks don't like store brand/generic/knockoff air-fuel/O2 sensors, or you've got a leak somewhere in your exhaust, either because bad gasket, crack, or hole from salt.

Note: While these trucks are sensitive to what air/fuel (upstream) and O2 (downstream) sensors you use, they're even more sensitive when it comes to cats. There's only three brands I've seen others report will work on our trucks without throwing intermittent codes.

 

So I've been driving the truck for just over a year and this is the first time a code has come up, so I doubt there's a crack somewhere down below. More than likely its just an o2 sensor that's bad. However, my obd2 scanner didn't tell me whether it was upstream or downstream, so I'll have to see if I can get more details from the scanner because I don't want to spend extra money (immediately) on a sensor that won't take care of the check engine light. I do plan to replace all 4 sensors in the future for sure.

 

Couple things.

First, you should really replace them in upstream/downstream pairs anway. i.e. Replace the upstream and downstream on one side, in this case, on your driver side pipe. In doing so you don't need to diagnose which is which, and if the upstream is failing, the downstream wouldn't be far behind (or vice-versa). The passenger side sensors can wait. You're looking at around $51 for the downstream and $41 for the upstream from a reputable vendor. Would you rather spend $400-600 to replace the cat instead, or $92 + shipping to replace the O2 sensors on the driver's bank?

Second, on using a scanner, the sadreality is, no scanner on the planet is going to see degradation (under-performance) in an O2 sensor. It *is* sensing what it senses, and that's that. You really won't, by any conventional means, know if it's a problem of the upstream OVER-reporting what it's seeing or UNDER-reporting. Or if it's the downstream. Basically, like every pencil does, sensors gradually dull over time if they don't fail abruptly, typically that would happen with an internal circuit and be reported as such. Sometimes, if your scanner supports realtime data, you can look for voltage fluctation out of the sensor as an indication it's behaving erratically. You can also get a laser heat gun and shoot the catalytic converter at the front and rear to measure for temperature differences, which can alert you to clogs inside the cat.

All you have in your truck info is "2001 red Tundra" which doesn't give anyone here enough details to provide more advice. I'm assuming you have the V8, but don't know what cab type or drivetrain (2WD/4WD) you have, so all I can give you is generic info. You should really update to give those extra details in your user profile under the "vehicle one-line description" here. We don't need to know what color your truck is to provide technical advice. Like, if your truck is 2WD, it uses completely different part number for the downstream sensors! This is why it's critical to include engine, drivetrain, and for wiring purposes we need to know if you're access cab ("AC") or regular cab ("RC").

But yeah. I hear you, you don't want to replace both. It's $200 (total) ballpark for upstream and downstream if you buy Denso brand from a reputable source that's not known to sell knockoffs (I'm looking at you, scAmazon and fleaBay).

Here are your part numbers for a 2001 Tundra IF your truck is a V8. It's the number starting "234-..."

Buy at www.summitracing.com or www.rockauto.com for the cheapest prices you'll find at a reputable vendor that has a verified supply chain, since counterfeits are so prevalent these days.

Note "RWD" is for 2WD trucks. This is the factory part. Pick the right sensor based on your drive. As long as you're not a rust belt truck, you can do this on your own. Get an O2 sensor wrench from the local auto parts store. DO NOT try to buy these parts locally, you'll pay twice as much if you can actually get Denso brand. Don't trust any brand EXCEPT Denso. (Maybe Bosch would fly, but it's roughly the same price)

​

 

Ya since the obd2 scanner isnt really telling me much, I was planning on replacing both. Also upon further inspection, I noticed that the air filter hasn't been replaced, so gonna replace that as well. I'm kind of wondering if its the air filter that may have triggered the check engine light, but overall, I'm gonna go after all possibilities.

 

I'm not going to say, "no way!" on the air filter. I've seen some weird stuff. But if you have a V8 in your truck, you have one air intake feeding two banks of cylinders, with one exhaust/cat off each bank. One intake + filter feeding two banks with one source of air, you shouldn't (theoretically) see a bad result on only one half of the engine, it should produce problems on both sides.

 

Well right now I'm going to give it til tomorrow to see if anything improves. Thankfully Walmart actually has a better deal than both Autozone & OReillys on air filters, so I went that route. Now of course I do plan to order myself some o2 sensors possibly next week (depending on how good my paycheck is).

Also I did notice that I am low on power steering fluid, so I'm gonna go by Walmart on Tuesday to top up on my power steering fluid. I'm also gonna have radiator flushed and put in fresh coolant there.

 

Note: Your power steering system doesn't use power steering fluid. It uses ATF.

I can't urge enough that, if you didn't know this, you should really reference your Owner's Manual. And if you don't have a copy, download it from Toyota HERE, save a copy, and read it. It calls for DEXII / DEXIII but anything DEXII or higher works fine, all DEX fluids are backwards compatible (higher number is OK for lower number, but not the reverse).

​

 

Well in all honesty I haven't looked at the manual yet, so thanks for helping to keep me from making a stupid mistake. Ya I'll go get some ATF at the store.