2011 2.5L 4Cyl Rav4 P0420 - At a loss for ideas

Hello everyone. This problem has a long history and I’ve pretty much exhuasted all ideas on how to resolve it.

In November of 2022, my car starting misfiring on the highway. After the spark plugs were replaced (apparently these were the original plugs, and they were being replaced for the first time at 189k miles… not good on my part), the dreaded P0420 appeared. In an effort to save some money, the downstream o2 sensor was replaced on the small chance it was that instead of the converter. This did not resolve the problem. When the old manifold was taken off the honeycomb inside the cat was visibly damaged, so its good that it was being replaced anyway.

The OEM exhaust manifold with the cat in it was replaced with one made by “Excel Exhaust” in May 2023. However, this too did not resolve the problem. Within the first day of having the new manifold/cat installed, again: P0420.

Take 2 on the downstream o2 sensor replacement, no charge from the mechanic. Again, P0420.

Take 3, upstream o2 sensor this time. Again, P0420.

Take 4, spacers on both o2 sensors. Again, P0420. (I realize this is not the correct method to use spacers in this case- as I’ve learned the top sensor is only A/F and not measuring catalyst efficiency… on to Take 5).

Take 5, spacers on just the downstream o2 sensor. Again, P0420, sometimes but not always. 9 times out of 10 if you clear it, it comes back, the other time the test shows “OK” but then is pending P0420 the next cycle.

My understanding is that the P0420 code is almost always the catalytic converter. The new cat + o2 sensors are all aftermarket.

I just don’t know what to do at this point. I’m considering trying to get one of those 90 degree o2 sensors with a so called mini cat in them, and trying that on the downstream sensor. Another thing I considered is replacing both sensors with OE Denso ones. Final consideration is that the aftermarket exhaust may just be that terrible that even with a spacer the sensor is showing that it just does not work.

Any suggestions for things I haven’t thought of, or ideas on where to take this next?

You do realize your vehicle has two catalytic converters?


Can confirm rear one was never replaced. Only the exhaust manifold. All of the rest is the original exhaust system.

There no sensor attached to the other converter, so would it even influence the code?

This is all based on a 2.5L I4 and not the 3.5L V6, since you failed to share the engine…

I am guess that is km and not miles, if so then that is about 117-118k miles and the sparks plugs are to be replaced at 120K miles, so that is ok…

I have a feeling your issue is a crap/junk cheap cat converter…
You can buy your Excel Exhaust converter for $158.00

The cheapest one that Rock Auto has is $420 to over $600 and $342 for there crap line of converters…


Topic edited with engine information.

It is not km, its miles. The car currently has 215k miles on it. It’s originally from new york and imported with me when I moved.

If the issue is that it is a bad converter then I have been very much ripped off by my mechanic… they charged me like $800 CAD or something near that for the manifold…

If that is a code for a miss fire, wires could also be suspect. I’ve used a Walker cat from rock before with no problems. Also you can ruin a cat with a miss fire in about ten minutes. Ask me how I know. $700;oem part.

Yeah 189K miles is a little over, but if not misfiring, should not have damaged the converter… If misfiring, then different story…

I think I would either have a hard long talk with your mechanic or find a trust worthy one that others say is good… Even at $585ish USD for the Excels converters I am seeing, that is high…

Yea thats what got me into this situation in the first place. Misfire on cylinder 3 due to spark plug. Was repaired before the converter was replaced.

P0420 Catalyst System Efficiency Below Threshold (Bank 1) pending/permanent is the only code.

I’m going to give you a clue.


I feel like you’re suggesting it’s the second converter, but is that even possible? The sensors are before it, and as far as i know it can’t cause this error code in this car.

That honeycomb that was damaged and coming apart in the front manifold converter went somewhere, as Tester is implying, the rear converter is next inline to catch the catalysts…

I see, would this however lead to this code if there’s no sensors back there?

Are you absolutely sure all exhaust leaks have been eliminated . . . ?

Does your car have California emissions?

If so, does the new catalytic converter meet CA specifications? It should have a “D- . . .” number stamped into the converter

Also, this applies to all catalytic converters . . . is the replacement part the correct part for the make, model year, engine size, emissions family, etc.?

There are many catalytic converters which appear similiar but are, in fact, not correct for certain applications and may result in P0420 . . .

Finally, I hope the mechanic is actually trying to diagnose this, instead of just being a glorified parts-changer . . . is he at least watching the oxygen sensor activity on his scanner?

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I will look into this idea again.

The car was originally sold in new york which i believe uses california standards.

The new converter definitely does not meet cali standards.

I’ve seen conflicting things online as to whether this would cause P0420 or not since some people claim the ECU can’t tell the difference, it will just fail emissions but no CEL. Others disagree and say it will cause this error.

As far as I can tell the converter is the correct one, it also is the one that shows up on excel’s website when you put in my car info.

They seem to have been actually watching the o2 sensor activity and going through things, or at least they claim they have been.

I can tell you from professional experience putting on the incorrect catalytic converter can indeed cause P0420 and an illuminated MIL

You believe your car has California emissions standards

Yet you know the new cat definitely does not meet California standards

That means the new catalytic converter is incorrect for your application


You definitely have to get those aftermarket oxygen sensors off and put the correct denso ones in.

Ask your shop to use their scan tool to display the pre-cat & post cat O2 sensor signals side-by-side. At a few different rpms, say idle, 1500, & 2500. Then post that photo here. The relationship of those two signals is how the computer decides if the cat is working correctly or not.

When an exhaust system is configured with two cats in series, it seems possible that if one cat fails, that could affect the exhaust flow through the other cat, and cause it to fail or appear to fail according to the o2 sensors.

Best to only use correct parts for the car, close as possible to the oem cat, Denso o2 sensors, but until the signal comparison is completed, suggest to discontinue fiddling with the cat or o2 sensors.

What is your motivation for solving this problem? Is it required for re-registering your car where you live? I’m presuming the engine is no longer misfiring, and there’s no other symptoms other than the p0420 diagnostic code, right?

Not rock!!! It sells the same garbage as everyone else but if you get a defective one, you are on your own. How do I know? I ordered an AC compressor from them once, the darn thing never worked. They wanted a receipt from a shop (which I didn’t have because I am a licensed automotive AC technician since 1992 so I replaced it myself), wanted me to pay more than 30% of the price for return AND would only replace it with the same “brand”. If I’m not mistaken, “four seasons”. I ended up buying the compressor from Denso directly for literally a few bucks more.

You need to spend some time reading post, I never said to order from Rock, I was comparing prices from everybody’s go to price place… I always recommend ordering from a local parts house, I compare prices a lot and after you add shipping they are not worth ordering from… Yes, I have ordered a lot from them in the past, but there is only 3 places I order A/C Compressors from and that is 1-1800, Ropples and Napa (I forget which brand) and always NEW, never reman… I have been doing A/C for over 30 years also… lol

So again, try reading my post and not taken crap out of context… :wink: