Car has Killed 3 catalytic converters



Every few thousand miles my engine light comes on. Code says Cat is below threshold. I’ve had it at the shop several times now and the car currently has its 3rd cat on it. The engine light has just come on again with the same code so it looks like a 4th will have to be installed now. Last time it was replaced they said that they ran testing but found no issues. Anyone know why my car might be killing cats?


Toyota is very peculiar about converters. Are you installing aftermarket, have you also replaced the ox sensors, did you check if your pcm has an update ? Is the engine running OK and did they check for leaks ?
Good luck, merry Christmas.


Why did you replace cat? did it stop running?
When light comes on it is just telling you a part of emission system is not working right, it does not mean you have to replace parts.
There are different sensors that tell computer how much gas,air and when ignition to fire.
When one or more of these are not working at certain levels it turns light and set a code to point you in the right direction.
Where are to taking it to get it repaired?


Are you getting the code P0420? If so, you won’t be the first one here that got that code, replaced the cat and it didn’t fix the problem. As many times as this has come up here, no one has posted back with something that actually fixed it. I’m working on one right now on my daughters car. I haven’t found the solution yet, but turning the code off usually fixes it for a couple of weeks or even a month. I only see her about once a month so progress is slow.


I also have been working with a Toyota Corolla with a P0420 code that comes and goes. So far, we’ve narrowed it down to gasoline at some particular stations. If she goes to certain stations, the light stays off. If she uses other stations, the light goes on. It’s pretty particular about what gas goes in it. We have not had the cat replaced yet. She was quoted $1,000 to replace with a Toyota converter and doesn’t want to spend that on a 10 yo car with 170,000 miles on it if she can avoid it.


What happens besides light coming on???
No start,missing,keeps dieing?
Trying to figure out how they got you to spend big$$$ 3 times just because a light comes on


My wife’s 97 Toyota Camry P0420 was the post cat Ox sensor. The front was replaced by the original owner in 2006 and I did mine last year. I used the same Ox that comes from factory, a Denso part, got from Napa auto parts in Atlantic Highlands. So far, thank God, the light is gone and the car passed inspection in NJ with a good cat monitor report.


The DTC code means that the results of the sensor inputs, as INTERPRETED by the engine computer, indicate the catalyst action is below threshold values. The first step is to verify, or disprove the computer’s assumption. That is done by testing the performance of the input sensors, and what gases are actually coming out of the catalytic converter. Surely, there are a few mechanics who can do this, somewhere?


He should only be spending BIG $$$$ ONCE and that’s if it’s out of warranty. The replacement cat should be warranted. These are probably defective cats that never came out of OEM aftermarket.

While someone mentioned cheap aftermarket cats being the problem, I’d be more inclined to think that it’s poorly designed OEM cats that are being used. The upper scale aftermarket producers have probably figured out the issue.


He may explore the possibility of a reflash on the PCM/ECM. I’m sure that there is some scan tool that resets the counters.

Just FYI for those who don’t know how it works, the system records the number of events where the rear O2 sees the same reading as the upper O2 sensor. The closer this count is to zero …the higher the cat efficiency. The higher the event count gets, the lower the cat efficiency.

This recorded protocol needs to be reset otherwise the PCM assumes that every event is one more in a series of them.


Turns out they are saying that the O2 sensors needed replaced. They didn’t catch the problem before for some reason. I already had this job done at 100,000 miles. After the mechanic showed me the old O2 sensors he said he believed that they were original factory parts. I’m starting to believe that the shop(Pro Auto Care) never put new sensors on in the first place. Might have used recycled parts or something.


Had the same problem with a 2001 Sienna LE/X van. Had aftermarket cat cut in and it threw a code in 6 months. Took it back for a free replacement and mentioned it may be the O2 sensor. Asked another shop about the code and they also said it had to be the cat and that the pipe and all three sensors should be replaced (about a grand in parts!). The second cat threw a code in one week. They then placed the post cat O2 sensor in the port in the back of the cat and so far no more codes (this was also free, service done about a month ago). Van had no performance problems at anytime during this process. If this happens again I’ll ask them about resetting the PCM/ECM, thanks for the tip.