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96 Lexus ES300 - Check Engine Code P0420 (Cat Efficiency)

I have a 96 Lexus ES300, with about 135,000 miles. The CEL had been going on and off intermittently, about once per month, for a couple of days at a time.

I took the car to the shop, where they diagnosed needing to replace the cat (P0420 code is cat efficiency). They tested and found O2 sensors fine, and indicate cat has no ability to store oxygen on rich side. After charging me almost $200 just to diagnose, wanted almost another $3000 (!!!) to replace the cat. Even the dealer is closer to $2000.

The shop said they refuse to use aftermarket cats as they are unreliable.

Meanwhile, my car not only runs perfectly fine with no noticeable loss of power or sluggish accelerator, but my gas mileage has actually improved, from around 320 miles between fillups (about 13-14 gal) to about 380 miles. I assume the O2 sensors are telling the system to run lean due to the cat issue.

Another mechanic tells me as long as there are no symptoms, to live with it for now.

I am happy to just do nothing for now, but my next state emission test will be in March 2010. I somehow passed the last one 5 months ago while the light was intermittent and the test occurred during a light off period. I'm surprised as the codes are stored and the CEL had been going on and off prior to the test, but I'll gladly take the test pass.

In the long run, I'll have to address this before my next emission test as I don't want the cost to buy a car anytime soon, but it's not worth paying thousands to replace the cat on a now 12-yr old car.

I'm not sure how to proceed, while my car is not only running fine, but better.

I guess my choices are, before the next emission test, to replace the cat with an aftermarket cat and take my chances, replace with a genuine Lexus cat and pay an enormous sum, or ditch the car and buy another one.

Does anyone have any experience with aftermarket cats, which to use or avoid, or should I not consider? I have also heard from folks who have taken their cars in for CEL issues, only to have the CEL come back on after repairs.

I'm not sure what to do. I'd hate to get rid of the car because of this.

Reply to
Dimitrios Paskoudniakis
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From what I have seen, aftermarket cats are a hit-or-miss proposition. People have had to replace aftermarket cats 3 or 4 times within a couple of years, so that doesn't bode well for their durability.

Cats fail because the catalyst substrate becomes coated with particulate matter over time, and if the exhaust gas can't come in contact with the catalyst, the gas doesn't get treated. In other words, the catalyst is still good, but there is no practical way of cleaning the particulate matter off of the catalyst.

If your car never or only rarely gets highway use, the old adage that it is good to blow the carbon out still holds. A highway trip gets the cat good and hot so more of the deposits get burned off and the higher exhaust gas flow blows stuff out of the tailpipe.

As to what you should do, if you decide to repair the car, have an OEM cat installed for best results.

Reply to
Ray O

Thanks. Coincidentally or not, I took a 10 mile ride on the interstate this afternoon, and later this afternoon the CEL went off.

Also, I live in Maryland, and their emission test program web site indicates that if the test fails, you get time to make a repair, and if $450 is spent and the mechanic certifies the repair, if your CEL is still on, you can apply for a waiver. However, the repair needs to be done within 30 days of the test, so I'll continue to monitor, and if highway travel keeps the light from staying on and no other symptoms appear, I'll wait until my next emission test in January 2010 to do anything.

Reply to
Dimitrios Paskoudniakis

Let us know how you make out.

Reply to
Ray O

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