Catalytic Converter Repair or Sell Car

I have a 08 Mitsubishi Eclipse Gs with 170,000 miles. The car is not a rusted anywhere and it does not have any dings. The car fax shows immaculate repairs by previous owners and myself. The car has matching cooper tires with new tires in the rear axle. I have experienced a check engine light that goes on and off for some time with codes P0421 and P0431. I tried cata clean and it did not work on my car.

Would you recommend OEM exhaust manifolds and a downstream catalytic converter?Aftermarket cats or headers with a high performance rear cat? The car has three catalytic converters. The exhaust manifold has the integrated catalytic converter and the cat converter on the rear of the car.

The OEM route would cost me roughly $3,000 with OEM O2 sensors, the header route would be less, but I would have to deal with O2 sensor problems. Would I be better off just selling the car ?

How long have you had it? It runs ok? Or not?

First, in my opinion, get a professional diagnosis.
I would recommend an independent shop that specializes in exhaust systems for an estimate.
Today’s car market may make more financial sense to repair than replace.

“Although the trouble code P0421 is related to your vehicle’s catalytic converter, it does not always mean that the converter is faulty. It could also indicate other issues, such as a circuit problem or a bad oxygen sensor.”

“The PCM uses the data from the oxygen sensors, which come in the form of voltage signals, to compute ignition timing and fuel delivery strategy. If the signal output from the oxygen sensor is lower, it means more oxygen is present in the exhaust (lean condition). If the signal output is higher, it means less oxygen is present in the exhaust (rich condition).

The PCM will store code P0431 if it reads that the upstream and downstream oxygen sensors of the catalytic converter on Bank 2 are reflecting similar exhaust oxygen concentration. It will also activate the malfunction indicator lamp.

Note: The definition of code P0431 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

Users have reported p0431 for the following makes: Mitsubishi (especially on a Mitsubishi Eclipse), Kia, Audi, Porsche, and Mazda.”

Quality aftermarket parts should be fine.


Why would you not install cheaper aftermarket cats on the car? Would be far cheaper than $3k, even with California emissions.

Do you live in a state or county that does emissions inspections? If not, can you live with the knowledge that while the cats still work, they don’t work as wel, as they did when new. That is what those codes mean.

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A well maintained, unrusted and otherwise reliable car with high mileage is generally worth repairing. Have you looked at the price of used cars lately?

Have someone connect a scanner or a scope/meter so the voltage signal from O2 senor after the cat can be monitored.

If it’s confirmed that the cat is bad, go with the aftermarket parts.

The reason the OEM cat costs so much is because it’s warranted for 8 years/80,000 miles.

You then have to ask yourself.

Am I still going to be driving the vehicle another 8 years/80,000 miles?



Concur, if OP likes the car, and testing confirms the cats are actually the problem, install aftermarket cats and keep driving. Even a $3000 one time expense is a lot less expensive than new car payments every month, plus higher insurance payments & registration fees.

Make sure any misfire problem has been corrected of course, otherwise the replacement cats may be damaged.

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Hello Everyone,
I had the car for roughly three years. I have not tested the cats on the car yet, but I believe it is the O2 sensor as the check engine light turns off automatically with no stored codes. The check engine light turned on this past sunday 8/15 and it turned off today 8/18 when I turned the car on to leave work.

The car runs fine, and there is a slight hesitation at acceleration to the car when running at higher speeds i.e. 30-40mph. A new car or slightly new car is tempting, but I am just going to fix the car. Whats your opinion on when to get rid of a car mechanically ? Kbb private sell is around $2,777

Smart man. Unless rust or body damage is an issue, or the vehicle just doesn’t meet your needs, keeping a car you already own is almost always the best decision. Even in a normal used car market, it usually costs way more to buy a different used car which runs well than it does to repair one that you already have. In today’s hyper-inflated used car market? It makes sense even to do major engine/transmission repairs to avoid having to buy something else.

There are literally only two times I would consider getting rid of a vehicle: when I need a different size or type of vehicle, or when it has broken down or been damaged to the point that it cannot be repaired again. Other than that, I’d keep what I have and let someone else go into debt “upgrading”.

BTW, the current average monthly loan payment for a typical car is approximately $450 per month. And many loans last for 6 to 8 years. Once you think in those terms, even expensive repairs like an engine/transmission rebuild can make sense. If a car needs a $3k transmission rebuild, for example, it literally only has to last for 7 months to cover the cost. In reality, the car might last for many years after that, resulting in huge cost savings.

When is your next vehicle emission test due? I drove my Dodge for 18 months with an intermittent P0420 fault code. No fault detected prior to the annual emissions test so the vehicle passed.

I installed a Walker direct fit converter 17 years ago and have had no problems.

Walker catalytic converter/manifold assemblies are $600 for the pair if they are allowed in your state and if you can install them or find someone to install them for you.

The high-speed hesitation could be a symptom of a damaged, partially obstructed cat.