When is it time to replace the cat?

Hey Everyone,

Been wanting a tacoma for years, and finally was able to snag a beat-up '97 4cyl with 238k miles. (I've basically been a full-time volunteer for the last 7 years so pennies are tight) I'm catching up on lots of little repairs, and after having it for a few weeks, 0420 reared its ugly head. I've always done my own maintenance on my vehicles, but don't have much training or anything. I probably know enough to be dangerous...but I do have pretty good mechanical sense. Things tend to work better when I'm around, but I don't want to overreach...

The guy I bought it from said he had it to his mechanic shortly before selling and he replaced the plugs and the O2 sensor. I suspect that code had come up before and that worked as a temporary fix. The guy at the auto parts place said, "You could try the O2 sensor...but at 238k miles, it's probably the cat that needs to be replaced."

I ordered a Davico model (affordable) from rockauto, and it came with this note saying:

DO NOT INSTALL THIS CAT!
To remedy a 0420 code...the OEM cat is supposed to last the life of the vehicle...check all other engine issues, both O2 sensors, decarbonize engines, inspect exahaust, EGR system, fuel system, OE converter, PCM reflash, ignition system, air intake...

and only if all of those things are taken care of should I even think about replacing the cat...

I don't really want to do all of that.

Am I just being lazy? Will I regret taking the old one out??
So...what ya'll think, should I throw in the new one? or keep poking around and replacing everything else??

I'm thinking to take it to the dealer and have them look over everything since the previous owner seemed like the wait-until-it-breaks kind of maintenance guy, and I'd rather practice preventative medicine. I imagine they'll have a thing or two to say about it, but I'm kinda gung-ho, and stingy...

Thanks for any thoughts/advice!
~Jacob

Also, I made a goofy video of me and my truck after I got it, just for fun. In case you're interested:
https://www.youtube.com/watch?v=WzxHDFxoRaA

 

Do you need to pass emission testing?

 

Fortunately I took care of that just before the light came on!

 

Ok, so you do. I would have suggested not replacing and don't worry about it if you didn't.


Yes check out everything before cutting out that factory cat as the aftermarkets just are not as well made. (I have my own conspiracy theory that ethanol kills them and will kill your new one too but no one seems to agree so.....)

That being said, they do go bad and Toyota seems to have a low tolerance on the parameters for effenciency.

Myself, I would buy a O2 simulator (edit: or build one, lots of threads and you tube vids about it) and go on but you may have qualms about polluting. (and they do 'stink' when cold)

In that case and after making sure everything else is in order before doing so, I'd replace it right before testing is needed again in case the new one goes again quickly.

I have found resetting my sisters Toyo van right before testing and watching the system *OBD scanner with 'real time', allows about a 15 or 20 mile window to go get tested while all systems are operating and "READY", yet before the ECU recognizes the cat problem. Bring it in nice and hot and the light out. There are lots of threads out there for what it takes to get ready to pass and sometimes it takes a couple of tries.

BTW: The cat is working, even when bad. You're not killing the environment with a bad cat, just not at 'peak'. + they seem to work fine when hot.

Edit: Just as any other time, going to the dealership and asking them to tell you what's wrong is just asking to be bent over and prob. won't help you in the long run.
Edit 2: What your states rules for testing? 1 'NOT READY' or 1 'NOT READY' as long as it's not the cat?

 

On my other vehicles Nissan 94 300zx, Chevy 97 z28, it has always been the O2 sensors not the Cat. And they all have about 200k miles on them. But none are Toyotas. I have also found that some replacement O2 sensors are not great either. Replacing it does not always work and you have to replace it again and then it does work. Just bad parts and very frustrating. And some mechanics may replace the wrong one in vehicles that have left and right bank O2 sensors and or front (upstream) and back (downstream) ones. They did that in my Camaro since the pipes both run to the right side and if you don't follow the exhaust back you will replace the wrong one and the pipes change sides.

If the O2 sensor is failing then it might throw the code. The Cat usually does not have any sensors on it. The ECU is using the sensing data from the O2 sensors to determine the CAT is possibly bad . On some vehicles they have an O2 sensor in front and behind the CAT. Your 97 looks like it does. I see upstream and Downstream O2 sensors available for it. If there is not a drop in emissions when it reaches the rear 02 sensor it assumes the CAT is bad when the rear 02 may be faulty. The ECU is just comparing the emissions at the Front O2 sensor with the Rear O2 sensor. There should be a drop after going through the CAT.

It could be the front 02 is not working and it is causing the fuel injection to make the engine run too rich and that causes issues with the CAT and rear 02 as it could be getting flooded with extra unburnt fuel from running too rich. But that could be the front of rear O2 reading wrong.

On most vehicles the front O2 is used to help tune your engine to be not too lean or too rich and the ECU adjusts the fuel mixture. The rear O2 is used to check the CAT efficiency but it is counting on the front O2 to be functioning properly as well in order to do that. So often it throws the P0420 when one of the O2 is in error, failing.

Unfortunately the O2 sensors look to be about $100 each. Some Code readers have live data where you can see if the front or rear O2 sensor is reporting suspicious data. They typically jump around some. If it reads flat, does not fluctuate, it is probably bad in my experience.


If you replace the CAT and it is not bad then that is a waste. Also if the O2 sensor is at fault and is causing your engine to run rich it could also cause premature failure of that new CAT too.

Or like the prior poster said. You can just ignore it and when it is time to smog reset the code, do the drive cycle to clear and ready all sensors and immediate smog it, preferably before the next day and give them the engine hot. Let it idle while you wait. My codes use to come back the next day or 3rd day after it ran another drive cycle and sensed the issue enough times to through the code again.

But doing that means the code will be setting the error light all the time and you will not be alerted that there is some other issue either. So I like to fix the codes if possible.

Maybe do some more web searching on P0420 code specific to your engine and vehicle and see what they say.

 

I am and have been having this same issue, haven't been able to figure it out yet. I replaced the cat a little over a year ago now but the check engine light has been on for months again now but there isn't really issue with how it drives. Mostly drive it on the highway and still get about 25-27 mpg so I've kind of ignored it. I have tried using seafoam top engine cleaner, cataclean, replacing the air filter, spark plugs, fuel filter and even PCV valve and EGR filter. I can't seem to figure it out. My next idea is too possibly take out the O2 sensors and attempt to clean them and see if something is wrong but I refuse to replace the cat again because I can't believe that it is already messed up. Does anybody have any other ideas for what I could do? I got it to pass smog a couple of months ago now and so I've ignored it but it does worry me that something isn't working right and I can't figure it out. Got a list of projects to do to my truck and no time to do them, want to show him some love though.

 

I would only suggest that you look into a really good OBDII scanner. I haven’t used one, but the one I’m looking at is about $100 and scans everything live. A cat, plugs, air filter, egr, adds up to way over $100 plus all your time. The OBDII scanner could save you time and money, not only on this repair, but the next. The one I’m looking at covers all standard AND proprietary codes, as well as ABS and SRS systems, so you could use it on your Taco and other family vehicles. Just be careful not to get one that only works on one brand, or only shows check engine codes, or can’t be updated via the web.

 

I realize it’s an old thread, but I just replaced my cats on my 2010 2.7L. My check engine light came on a month or two ago. I started noticing that the engine seriously liked power. Like I had difficulty reaching the speed limit AT ALL kind of lacked power. I got to thinking that maybe a cat was clogged because the engine was fine at low RPM and when puttering around town. I pulled the cats. The rear cat looked OK from behind, but of course you can’t get light on the other end to see if it’ll shine through. You can’t seen the from cat die to the bend at the flange. I stuck a leaf blower on the end and determined that it wasn’t flowing as freely as I though it should have been. After setting the cats and pipe back on the ground I noticed some grey powder at the flange that the leaf blower had blown. I shook the flange around a piece of cat fell out. I cut the first cat out and it was just an empty housing. I cut the second cat out and it was plugged with bits and lives of the first cat. I welded in a very large 2.5” universal cat(stock cat had a narrower body and smaller inlet) and eliminated the second cat, so it’s no longer legal on the highway, but that’s OK because I just bought an ‘08 xtra cab for daily use and am only keeping the ‘10 as toy(it’s been bounced off of every rock in the state and no one would pay me anything for it) The check engine light turned off and the engine is back up to normal power. Frankly it feels more powerful than when new, but it may just be because I had become accustomed to it being weak due to the plugged cats.