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Toyota Corolla Catalytic Converter Assembly


I have a 2006 Toyota Corolla CE. I am in need of a new catalytic converter to pass my upcoming PA state inspection. That had actually been diagnosed some months ago via computer code. At my latest visit to the local garage, they indicated to me that I would need a new air intake sensor, as well as a whole catalytic converter assembly, the latter of which is almost double the cost of their previous estimate for a catalytic converter alone.

Having patronized this shop many times before, I have no specific reason to doubt their expertise or judgment. But, I would like to ask a couple questions:

  1. The price they quoted to me included the standard Toyota brand catalytic converter assembly. When I do an Internet search for catalytic converter assemblies or catalytic converters, I get some greatly varying prices. Would it be safe going with a non-Toyota catalytic converter assembly?

  2. Speaking of catalytic converter assemblies, what is the difference between a plain old catalytic converter and a catalytic converter assembly? When I search for either on the Internet, I get the same results and prices.

  3. Any other questions you feel I should be asking, please feel free to answer them!



I was going to ask you question number 2. What, if anything, is the difference? I’ve never heard of a catalytic converter assembly.

It’s very unusual for a car this new to need a catalytic converter. Often a malfunctioning cat will work correctly with replacement of the O2 sensors or some other, less expensive repair.

There is no code that says “replace catalytic converter.”

Can you get the actual diagnostic code from your mechanic and post it here?

if you do need a catalytic converter why isn’t it being replaced under warranty?

7 years or 80k miles and the dealer will replace it free.

The assembly probably includes the flex pipe and tail as a complete assembly. It’s very difficult to replace only the cat on some welded systems due to space constraints. The cost of labor will quickly exceed the cost of the whole assembly if they have to take things out, cut it apart, fixture it, weld it, reinstall, etc. Some of the better muffler shops have devised their own aftermarket assemblies and they are a lot cheaper than the OEM assemblies.

The emission components will be warrantied for 8yr/80k miles IF you haven’t contributed to their demise through negligence (lack of maintenance) or misuse.

The actual diagnostic code is P0420. And, what I referred to as the “air intake sensor”, is actually called the “mass air flow sensor” on the mechanics’ sheet. Thanks!

Oh, one other thing, regarding warranties … I have 158k miles on the car.

With that many miles on the car, I would start with the MAF sensor, and also replace the Oxygen Sensors first, and see if the P0420 code goes away.

It will save many many hard earned dollars if it resolves the issue.


Thanks! I appreciate it.

Does anyone know, would the O2 sensors be considered part of the catalytic converter assembly, or separate parts?

An O2 Sensor Screws Into The Converter Or Exhaust System. It Is A Small Part.


On this vehicle you have two O2 sensors (oxygen sensors), one in front (upstream) of the catalytiic converter and one behind (downstream). The car’s computer compares the two signals to determine if the converter is working effectively.

I’m unsure of excatly how this system is configured, but Toyota will often use multiple converters in series on a single system. In my tC there are two, the only monitored converter being built into the exhaust manifold bolted right on the engine. They do this to heat the catalyst faster, because its effectiveness is directly reliated to its teperature. The first O2 sensor is screwed into the manifold and the second in the pipe further down the system.

The Mass Airflow Sensor is a whole different unrelated part. It measures the amount of air coming into the engine. It’s located in the intake, just after or at the back of the air filter box. It’s a heated sensor, and at your mileage needing a new one would not be unusual.