Dreaded P0420 CEL UPDATED post #59

Hey everyone. Finally got my dream vehicle, a Tacoma. Picked up a 2002 SR5, extended cab, 4X4 automatic. Has 107,200 miles. Runs perfect. I live in NY but found this one in Vermont (all I could find locally had 200k+ miles, was rotted out or I couldn't afford it).

Driving home this Saturday the CEL came on after about 15 minutes. I borrowed a scanner this morning to find....P0420.

I bought it with a brand new converter, visually confirmed and have paperwork for it. It runs flawlessly. No hesitation or shuddering. Got 19.5 MPG on the way home too.

Before I throw part$ at it I'm wondering what everyone's thoughts are?

Looked at upper and lower O2 sensors and I'm 99% certain they are originals. Read stickies and FAQs all over (clean MAF, TB and sensors, swap plugs, etc.....) But what is the RIGHT way to diagnose this and fix it properly? NYS requires an annual inspection before I can plate it. I'm on a temporary VT tag for now.

Thanks in advance everyone.

 

Clean the MAF and the TB. Swap plugs because they most likely need to be swapped anyways. If that doesn't fix the problem, your only option is for new 02 sensors.

 

Thanks. I'll start with that and go from there. Never thought to ask if plugs were new. Maybe I'll clean MAF and the TB first, seems cheapest (after I search how to properly clean them), reset code and if that doesn't work, try plugs and wires.

I appreciate the guidance. Hate throwing time and money at "maybes".

 

Definitely. Always start with the cheapest routes when you're guessing lol.

 

Before messing with the cleaning part, I would probably inspect the exhaust system (flange gasket or poor weld point) especially if the cat was recently replaced. if it's a weld on cat, the weld point might leak. I see it all the time, if shop don't remove piping off, the top side usually leak because of weld angle. If it's a new direct replace cat, check to see if flange is leaking. LAST, double check the rear oxygen sensor to see if the harness is even plug in, not torque on properly, does it have a gasket, or a leaking gasket.

Just my opinion. Why start removing parts off when you already confirm the cat is new. Exhaust leak can cause p0420.

Also, check your intake tube after the maf and vacuum line or vacuum port. They can also generate p0420.

Installing new fuel filter, air filter, spark plugs, diff/trans oil etc is always a plus cause you know it's been done. At least I do it to all my new to me vehicle. Sense of knowing is better than not knowing.

 

Just cleared my P0420 code. I was planning on replacing both cats as well as the 02 sensors anyway. I ended up replacing only one cat (TRD Y-pipe wouldnt line up with fwd cat) and the 02 sensors and it cleared. If all else fails you could buy a URD 02 sensor simulator and CEL go bye bye.

 

check for exhaust leaks! around the manifold

 

Thanks everyone. Depending on how busy I am today, I was going to dive into this.

Question on exhaust leak though: wouldn't I hear it's leaking? Especially around the exhaust manifold (the audible *tic tic tic* is usually a dead giveaway). This exhaust seems perfectly quiet. Will double check around new cat though just at the off chance the bolts aren't as tight as they should/could be.

 

It needs a cat. Do not replace plugs, filters, etc.. an intake leak at the maf will set p0171 or p0172 (lean codes). Just because the cat is new doesn't mean it's got enough catalyst material in it to satisfy what the pcm is looking for during catalyst monitor (it compares O2 sensor readings before and after the cat). If it is a universal weld- in cat from AutoZone or o,Reillys it is junk. It has to be OEM..

 

Remember the manufacturer does not want the converter code to set . up to 8 years 80,000 miles it has to warranty the cat for free so it's going to exhaust every possible test before it gets to the converter test. if you had a problem with spark plugs the engine would run rough. if you had a problem with oxygen sensors you would have oxygen sensor codes . if you had an air leak you would have rich or lean codes . see where I'm going with this? it needs a cat bite the bullet get a factory converter and you will be done if you try to dodge around with tune up stuff you're wasting money converters are expensive but it's just part of owning a car in the 21st century

 

Good to know (sort of). The dealer I bought it from is a small 8-10 car lot place. He showed me the invoice for the work and I know for certain it's not OEM. It was done by a local shop. Now my fears of chasing my tail and throwing unnecessary parts and time at it are becoming reality. May end up going the O2 simulator route. I can't imagine an OEM car is cheap.

 

Can you pass NY test w/ 1 'not ready'? if so, there's your cheap answer.
I agree aftermarket cats are crap, new factories are expensive.
If cat is good you can make a 'fooler' for the rear O2 to not set off the light,($5 at Radio Shack) if cat is no good the TRD simulator will work.
"These cats are just too dam high".

 

Here's what it looks like (pardon cellphone pic). Don't know if you can tell what it is by looking at it brand wise.

 

In theory, since the cat IS new, just not up to snuff for the ECU. The resister and capacitor (cheap-o simulator) should work.

It did on my Sis's Sienna even with a so-so cat.

 

Good point Crux, NYS inspections are pretty tough. If the computer can detect something has been bypassed as you seem to imply, it won't pass. Also can't reset CEL and run to get inspection done before it comes back on. Computer knows that trick too. Needs 50-80 miles of drive time to reset everything and by then I know it'll be back on. Dang.

 

spray some soap on cold or semi-warm pipes and see if you have bubbles?

 

The cheapo simulator is for that purpose, to get the 'not ready' status off.
Are you allowed 1 'not ready'?
Many places are.

The computer can't detect something that slows inputs back to normal readings.

 

Sounds no different than Texas.

 

I can call and ask a good friend of mine. Good point. Also just now noticed your symptoms and diagnosis post a few above this one. Makes perfect sense. *Sigh*

 

Sorry to bounce around. Are you saying I would currently be experiencing a "not ready" signal and the O2 sim would remove that? Obviously a lit CEL is a failure however if the O2 sim simply turns that light off AND the computer is still saying something is going wonky, it'll fail then too.