P0420 is it always a bad cat?

Found a few exhaust leaks at connection points. Once spot is after the first cat and before the second. The other connection is after both cats. The leak before the second cat is small, do you think that small leak could be causing the p0420 code?

 

it does not take much. As the exhaust gets hot the leak will expand.

Replace the gasket and hope that fixes the problem.

 

There are a couple of ways to test the cat. If you hear rattling, it's time for a new one. Furthermore, if you stomp on the gas and get a flashing check engine light and can't seem to get over a certain RPM, your cat is likely the culprit.

I suspect addressing your exhaust leaks will clear a few of those codes though.

 

Ahh, OK, she needs to pass smog. Couple of ideas that have worked for me in the past and not all fixes work on all tacomas due to differences in exhaust configurations.

There is a post here on the 1st gen forum where you make a electrical gizmo that modifies the rear O2 sensors signal to the PCM. This tricks the PCM into thinking that the cat is doing its job. There used to be a company that manufactured a plug in version that works great but it has been discontinued. The $100 spent on that was well worth it.

There is another trick where you thread in a spark plug spacer into the rear O2 sensor hole to space the rear O2 sensor out of the exhaust stream. This reduces its sensitivity and it will take a while for the P0420 code to reappear.

in my experience, it takes time for the P0420 to actually trip. I usually do my smog monitor runs at night when there is no traffic on the road. I drive the smog problem vehicle around until all of the monitors have run and it is ready to smog. I will drive it immediately to the smog shop and park the truck so that I am the first one in the AM. I dont want to take the chance that the code will pop by driving it home then to the shop in the AM. Doing it this way gives me time and that is what you need until you figure out how you want to attack the issue. Am I a smog nazi, no, but multiple hundreds if not thousands of dollars put into an old truck sometimes just isnt worth it.

The next question is why is the P0420 happening? Is/are the cat(s) damaged because she burns oil or because they are just old?

 

P0420 cleared itself after I replaced the gas cap

 

A catalytic converter code cleared after you replaced your gas cap? Is that not odd?

 

yeah thought the same, P0420 is notorious for coming and going for awhile before it sticks around. And clearing a code just resets the emissions cycle which can take awhile to complete itself, when it does that code will eventually come back.

 

I replaced what exhaust leaks I found, and drove about 40 miles today. I cant really check the manifold due to the heat shield blocking it. Codes persist. I am bringing it to the stealership Monday for a exhaust system leak test and to pump some smoke in my evap lines. Figured they could tell me if the either of the cats are bad.

 

Heat shield has two bolts on it man, ezpz. My manifold was cracked on my 02. If you haven’t read through this sticky, you should:

https://www.tacomaworld.com/threads/addressing-some-common-misnomers-of-the-p0420-code.396763/

Also cat monitors take a while to complete, maybe give it a few days before giving up. There’s technically a specific driving procedure to complete it but mine ran and completed after a few days of regular driving.

 

If it's only 2 bolts I'll take them off and check. Also to be clear, all readiness monitors are showing complete now despite still having the p0420 code and 3 other EVAP codes. So it has the capability to pass emissions test if only the codes were gone. I also want the dealership technician to be able to read the codes when I drop it off so I think I'll wait to reset them until after that

 

Just FYI in my state a 2002 can pass with just one readiness monitor not ready... Food for thought

You will fail if evap isn't taken care of as well, and evap is an easier diagnosis

 

The CARB number IS actually stamped on the CA legal cats.

Now, whether the smog tech Eben checks is another story... but the CARB number is there on the CA legal cats.

 

Fix those and it should go away.

 

Do you think the code may have came up because I didn't replace both o2 sensors, only the upstream one. I replaced the upstream one with the correct denso part, not sure what was in there before as it had no markings and also not sure what brand the downstream one is.

 

No, the programming in the PCM doing what it is supposed to do. The front 02 sensor measures the 02 content as it immediately leaves the motor and depending on that reading, modifications are done to fuel, spark timing etc. This pattern is an irregular “sawtooth”. The catalytic converter(s) are 02 storage devices. Any unburnt fuel is burned up in the cat(s) and converted to other gases. The rear 02 sensor measure the 02 content as it leaves the cat(s). If the cat(s) are doing their job there will be a steady flow of 02 out of the cat(s). This 02 sensor reading “should” be relatively flat steady line. If the rear 02 sensor signal mimics the front 02 sensor then the convertor(s) is/are not functioning efficiently, hence the “catalytic convertor efficiency” code. The strategy and programming behind this is much more complicated than my simple explanation but you get the basics of what is going on.

 

Thank you for that explanation. The truck has just been dropped off at the dealer for further diagnosis. Will update thread when I hear back.

 

Soooo... Dealer called.
Apparently they say the O2 sensors are not within spec, even the new denso one and recommend new Toyota O2 sensors and two new Toyota cats. For a grand total of about $4500.

They also said that in relation to my EVAP leaks I need a new gas tank and filler neck and other gas tank supporting lines. $2400 for all that.

Right now I'm thinking I'll try replacing the tank myself and for the exhaust stuff I don't know. Needs to pass emissions, no sniffer where I am just OBD2 readiness. Could I cut out one cat (I have two) and trick the o2 sensor somehow?

 

There are o2 sensor "defoulers" you could try installing that might get you past the emissions part of the inspection, assuming there's no visual check. Personally I'd buy the walker or magnaflow cats and convert everything back to a bolt together system with fresh gaskets. I like being able to replace parts without cutting or going to an exhaust shop.

On the gas tank, you can get a replacement Spectra tank for around $300, add in a fuel pump and some replacement hoses and gaskets and you're probably around $500 there. It's not a difficult job, just time consuming and you might need some help removing the bed. I took a few pictures when I did that job that might be helpful: https://www.tacomaworld.com/media/albums/2020-12-gas-tank-decrustification.63925/

 

I just ordered an o2 sensor "spacer" a 90 degree fitting that spaces the O2 sensor out of the exhaust more. I think that's the same thing as a defouler. I honestly find it hard to believe the cats are bad considering they're less than a year old, although who knows what brand they are. I like the idea of a

$175 magnaflow 99005HM : 2.25"/2.25" inlet/outlet, HM grade, universal fit (EPA compliant)

magnaflow 99005HM cat.

As for the gas tank, do you think it's necessary to pull the bed? Assuming the straps will have to be replaced anyways I could just run the tank almost empty then unhook it right? Of course pull what lines I can off of it first and slowly lower it with a jack.