Dreaded P0420 CEL UPDATED post #59

They are telling me with 100% certainty it's the front cat so I wasn't going to continue to look at the other stuff. Maybe they are wrong? Don't know.

Hate to ask since I know it's a no-no but..... will the O2 sim mask my front cat issue? We're talking a repair that's 1/8th what I paid for the whole truck. Based on my reading, if I get a cheaper/aftermarket cat it may not fix it anyways.

 

Good luck. I ain't got nothing more to input here.

#byefelicia

 

Have I committed some sort of taboo and am unaware? *Confused*

 

I think he was a proponent of the o2 sensor fooler thing and aftermarket catalytic converters.

I thought that the O2 sensors just read the front cat to begin with? Doesn't make sense to replace the rear. Also I've had success with aftermarket Cats and some you can buy as bolt-ins. Maybe call some exhaust shops and see what they use. They typically will be cheaper than the Stealership.

 

Not quite. But if he's gonna take the stealerships word and not do any work himself I have nothing else to add.

 

If the truck is still running fine with no misfires or loss of power then I personally would just let it ride for a bit. A code being thrown from a faulty CAT is a minor issue and won't greatly effect the truck if driven for a while that way. Start saving your pennies, and eat ramen for a few weeks till you can get the CAT fixed.

 

You can get parts MUCH cheaper aftermarket. Unless you are in CA I would just change it out yourself.

 

Closed up shop for the day. For now I'm going to clean MAF and TB since based on my reading, it probably needs it.
My thought is that if it isn't the front cat why would the dealers have me invest in a $1400 repair that doesn't work?: I have also repeatedly said I don't do this stuff which is why I am asking in here.

Had I said, "Screw you guys. I'm paying $1400 against the advise of those who have experienced this." then I could see the reaction. I also run a motorcycle forum similar to this. Over 6000 members in about 14 countries. I understand not getting through to someone who won't listen. I'm not that kind of person.

 

Green, I thought everyone was of the conclusion that aftermarket cats don't work properly and that OEM was the only one to invest in?

 

FWIW I would still consider doing your O2 sensors before the CAT. Those sensors are actually very fragile and from the look of your first pic it looks like they haven't been done for a while and could stand to be changed anyways. Also had people tell me with absolute certainty that I needed a new CAT when I had this exact same code. Did 02's first (figured they needed to be done and went cheaper option first before CAT) and haven't had a CEL since.

 

Since they look like they are old, possibly originals, I'll replace them as well. From what I've read, Denso is the only way to go so I'll order them in a few.

*Edit* I guess I wrongly assumed that when I asked the service manager directly, "You are certain it's the front cat and not an O2 sensor or something else?" and he answered in the affirmative, I had my proper diagnosis. Had they said, "You need a front cat and while we are in there, we'll replace the O2 sensors as well." then I'd be slightly suspect.

 

My anecdotal experience with my old Subaru. I took it to an exhaust shop and they confirmed the cat was bad. So i had them replace it (aftermarket one). I drove it home and the CEL came back on so I replaced the O2 sensors and the CEL went off and stayed off. I wish I had replaced the O2 sensors first just to make sure I didn't have a bad one causing the CEL.

I only went through with all that so I could sell it though. We only have to smog it on change of ownership where I live. I bought the car with 100K on the ODO and the CEL came on almost immediately after I bought it. I determined it was the cat/smog something and I put another 80K on it with the CEL on the whole time...

 

[QUOTE=" Based on my reading, if I get a cheaper/aftermarket cat it may not fix it anyways.[/QUOTE]

Just a little note from my experience as I just replaced my whole exhaust, I took both front and rear cats out and replaced it with a single magnaflow cat. Also replaced the O2 sensor and went with NGK not Denso, and so far after almost 1000KM have not had an issue. I had the P0420 code keep coming up but my exhaust also rotted away halfway back so thats when I just re-did it from headers back. It cost me about $700CDN all-in.

 

An exhaust leak for example, would show that the front cat is bad.. Notice the placement of the O2 sensors. The code is thrown because the rear sensor is reading the oxygen content is incorrect(too much/too little Oxygen). This is why we keep saying check for exhaust leaks. The stealership would suggest a whole new pipe/cat because it would correct the problem, example an exhaust leak, and it's money in their pocket.

 

Ive not heard of any issues of a quality aftermarket cat.

I would certainly check your sensors, perhaps switch them or replace just one and try it in both holes.

Be weary of cleaning your throttle body, depending on wear patterns, It can be worn and create a "leak" between the flap and the body. Mine idled at 2500ish rpm. It was pretty sweet.

 

FYI, there is a difference between the two O2 sensors. The upstream will not work in the downstream, and I know from personal experience, the downstream will not work in the upstream! The upstream has a heating element in it and the downstream does not. If the computer can not read that element heating up it will continue to throw that 0420 code. I am not afraid to admit I screwed up and just bought 2 O2 sensors thinking they were the same. Ended up with 2 downstreams and CEL persisted. Found a thread on here that explained the difference and bought the correct upstream and haven't had a problem since.

This is the thread I found. It is stickied on the 1st gen tacoma page. https://www.tacomaworld.com/threads/addressing-some-common-misnomers-of-the-p0420-code.396763/

 

the front O2 does all the magic. fuel trims, and I'm not even going to pretend to know what else.
the rear, really just tells the ECU that the cat works. Does no adjusting.

The TRD simulator (80 bux, I've heard) is for people who have done a cat delete and want the engine to appear as normal.

Is it different than a resistor and capacitor.....up for debate. No one (that I've seen) has torn theirs apart. Since TRD sells it as a 'fix' for factory built mods, it prob. is more complex. I suspect if it was much more complex, it would be more than 80 bux though.


I thought and you affirmed that since you just bought the truck, (and it sounds like a deal for that low mileage, even with trouble in paradise) you could do something cheap just to get it legal in your state. then fix it at leisure. You may find a complete exhaust somewhere. Point is, you have options, cheaper options. Short term at least.
It WILL take some time and effort to pin it down and play with. But as many on here have said, they dropped theirs off at a dealer hoping to just throw money at it and still got a code afterwards.

I have a lot more to add (and I deleted) over the disparity of what mods are considered 'cool' vs. ruining your truck (exhaust, mechanical and electrical) but I guess I could start my own thread.

You sure titled this thread right though, it's dreaded and fooled many, many times.

 

I installed an aftermarket cat on my wife's truck 6 years ago. No check engine light yet.

Those CEL will drive me nuts. If the light came on, I would have spent the coin for a factory unit. I gambled and got lucky.

 

Now this made perfect sense and I appreciate it.

As of now, I've done what I would consider low cost maintenance items that may have needed doing anyway. I cleaned the MAF with the proper cleaner. Looked like a dirty matchstick in there so I'll guess it needed it. Also removed and cleaned the throttle body. Even sprang for a brand new toothbrush to do it. Pulled the plugs and was pleasantly surprised to see they were in fact, new.

Took a few pics. Will upload tomorrow. Even found some french fries (yes) in the airbox ahead of the filter. Airbox was warm and so were the fries. This will make a great snack on my hour drive home.

While working I had the battery disconnected so naturally the CEL is out for now. We'll see how the drive goes. It's idling perfect and started instantly.

Tomorrow afternoon, with a cold exhaust, I'll fire it up and check for leaks as best as I can. If no leaks and CEL returns tonight or tomorrow, I'll go for new O2 sensors starting with the rear. Fingers crossed.

 

Had a few mins so thought I'd share:

Mmmmm. These are still warm.


Dirty MAF (forgot to take a clean pic)



Dirty throttle body. Used proper cleaner for it, fresh toothbrush (I'm a big spender).


All clean.


Plugs looked perfectly fine more pizza money for me since I won't need to get new ones.