I have been fighting emissions problems with my rig for the last 3+ years. My 4runner is a 1500/mile rig with 312k on it so I haven't put much effort in it. Its time to seriously considering letter her go. It threw a p1135 the other day. All the wiring checked out, the heater coil checked out. I think the connection was poor. Put it back together and its cleared.

Then it threw a p0420 again. It did this 3 yrs ago too, I forget how I fixed but I did and obviously it was not a long term solution. Popped up again when this year when smog was due again. I "fixed it" by getting a new sensor and I un bolted the cats, soaked them in degreaser as a hail mary. It passed smog and was ok for a couple hundred miles. But it has come back.

CARB compliant cats are $550 and $520 for the weld in respectively. Obviously I want to do this as cheap as possible. I plan to DIY. Can I get away with replacing just one, or do I need to do both? I am also open to ideas.

So I guess Cali needs all emission items to be in Ready status?

Texas allows one not to be, only one. I get a 420 every time I crawl a few miles, like clockwork despite new cats, A/F and O2 sensor.

Since covid I haven't even bothered going for an inspection since '20, cops just don't care here anymore, is that an option for you?

Are you saying you have replaced everything and the code still comes back?

Unfortunately, I wouldn't be asking if that was the case. All sensors need to be "ready" except the evap. Problem since mine is an 02, once any code pops up, it disabled Trac and VSC as well. I am sure your 01 does the same as well.

Yes but only when I crawl a few miles first at low speeds under 10 mph or so, if I avoid that I can drive thousands of miles with no codes, crazy.

I can attest to this. My VSC TRAC and VSC OFF lights show up when my truck has a P0420. When it's off, the VSC lights are off. If I get any other codes those lights don't come on with the CEL. Just my experience with my 01.

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Are having to top off your antifreeze at all?


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If the cel lights Trac and vsc are instantly disabled [01-02]

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no, its not using coolant.

Back to the original question. For those of you in CA, can I get away with simply replacing just one of the cats? I guess my biggest question is that legal assuming I get a CARB Cat.

You won't be able to remove the cat as you'll more than likely fail visual inspection. The good news though is that our state does allow for 1 test not to be completed. I'm in the same boat as you though with the same code. So far in the past 2-3 weeks I've cleaned my MAF, replaced my knock sensors and (unrelated) swapped out my alternator. I've been able to get all tests to completed except for Catalyst which is what throws the P0420 code for me. What I've been trying to do is get all except for that code to complete and then immediately rush to a smog center, I think I did that about 3 years as well. My only concern, and I'm not sure if it's valid or not is that I will get the P0420 code as "pending" and I'm not sure if that will be an auto fail or not. If you look at this screenshot I took on my OBDII scanner, the car is ready for testing for me without that one test but as soon as I try to get off the freeway only a few feet from the exit the other code comes up. I've been able to get the evap test to complete in under 5 miles from my starting point so I know it's doable, it's just a huge hassle.

Oh I do not want to remove the cat completely. Just replace it. You can get CARB approved cats from magnaflow for example, they are just $$$. I was actually just reading your post and someone mentioned the gaskets in the exhaust. That is a great idea of something I am going to check. I know they are cheap.

Yes I am aware that one test can not be complete. thats not the point of fixing it. I want to actually fix it once and for all.

So you want to replace the first catalytic converter, but leave the factory second catalytic converter in place?

Well I was going to replace the 2nd on because it's the easier one. But yes.

It could be enough to get it to pass, but it might not. Even if it does pass who knows how long it will be good enough to get it to pass. If anything I would replace the first one because the first catalytic converter does the most work.

I wouldn't be surprised if there was a 4Runner group that shares a nice dual-cat CA system that they install on each other's rigs every 2 years for testing and straight-pipes it the rest of the time. Scoundrels. Anyway, on post-2000 rigs I'm not sure how much of a visual they do because all emissions data comes from the ECU not a tail-pipe sniffer....I've been lucky so far - knock on wood. Get the cat(s) hot before the test whatever you do - they work better hot. I'm just about to get my smog done before the cat-jackers find me. Then I've got 2 years to worry about it....

Its time to post it up for sale unfortunately. ive put <3k miles on it in 3+ years.