To (catalytic) convert or not

I’ve read some of the previous discussions about catalytic converters, but I’m still unsure. Here’s my story.

A couple of weeks ago, my CEL came on in 1997 Corolla with almost 115k miles on it. My neighbor used his scanner and said that the exhaust system was working under 80% efficiency. He said I might need a new catalytic converter, and to start the search for a reliable shop to work on the exhaust system. The light went out after he checked the computer. It came on again about a week later, stayed on for about five days, then went out again yesterday, although I have done nothing except consult with a mechanic who said it would cost about $200, and that the oxygen sensor may also need replacing.

Other people have told me they’ve driven for years ignoring the CEL and that the cat converter is a scam by car companies.

I’m about due for timing belt change, and am willing to do both at the same time if needed, or is this the beginning of the end and is it time to just pack it in and get a new car now before I retire?

Catalytic converters may be a car company scam, but if so they have scammed it into the laws, and penalties in some states can be harsh for bypassing them, if that’s what you mean, People who say things like that are not your friends.

A corolla, if the body is generally in good shape, 115,000 miles is nothing – assuming you have maintained it at all close to requirements.

Personally, assuming you buy a car with high reliability, (check Consumer’s Reports, and ignore the folks who claim they are paid for good ratings, these guys also are not your friends,) buying a new car before you retire is often considered a good idea, since you can schedule your retirement to cover the financial issues. It can be harder once you are committed to retirement to flex on a big expense or to recuperate from it.

Once you retire, there is no over-time work to make up an expense, but as long as you are working, you can do things like that.

This is separate from the car repair issues. Many people i worked with before I retired, did just that – get new cars, good cars, before they retired so they were solid for ten or more years.

“The cat converter is a scam by car companies”? I hadn’t heard that one. That’s cute.

The cat converter is not a scam by car companies. It’s there to reduce emissions in the exhaust. The main things it does are reduce oxides of nitrogen (NOx) by passing the exhaust pass a honeycomb plated with heated platinum-palladium/rhodium. This “catalyst” causes the notrogen and the oxygen atoms to seperate. It then reduces carbon monoxide (CO) by providing an opportunity for carbon monoxide molecules to “pick up” now-freed oxygen atoms and become CO2.

Now, the deal with the oxygen sensors…
You have an oxygen sensor “upstream” of the cat converter that measueres the oxygen in the exhaust stream and “tweaks” the injector output (via the ECU) to maximize efficiency and minimize emissions. You have another “downstream” of the cat that measures the oxygen after it’s been through the converter, basically compares it to the upstream output, and tells the ECU if the converter is not doing its job. If it isn’t, the ECU lights up the CEL.

The code that your friend’s scanner read is the one that the computer has stored as to the performance of the cat converter. It’s saying that the converter’s efficiency has deteriorated, which it can tell by comparing the aforementioned signals. The reason the mechanic said you may also need a new oxygen sensor is that the same exhaust stream thing that caused your cat converter to deteriorate can also cause the oxygen sensor to deteriorate. Both need surfaces free of coating and contamination to work properly.

These things are normal wear & tear. They do not indicate a need to get a new car.

Now, as to those “other people” who drive their cars around for years with the CEL lights on…you don’t honestly think this is a good thing, do you? Good. I didn’t think so. In addition to warning you of an emissions system fault, the CEL light is there to warn you of a potentially engine-destructive condition.

Do you know what trouble codes are causing the check engine light to come on? Are there any other symptoms other than the occasional CEL coming on?

I don’t know what your neigbor was scanning your car with, but you need to get the trouble codes off of your car and post them here. Maybe “exhaust system working under 80% efficiency” is a rough translation of a trouble code (although it sounds like technobabble to me)-- even if it is, that could be just as easilly be caused by a faulty 02 sensor or a rusted exhaust component somewhere upstream of the 02 sensor. Catalytic convertors almost never just go out-- they can either be destroyed by physical damage or by serious engine-tune isses that get ignored for a long time. If you post those codes here, we can probably give you some specific possibilities, but you will probably need to have a mechanic actually invest some time diagnosing the thing.



Thank you. Now if I can only get this system to stop ramming my paragraphs together!

I would like to add that a constant check engine light is usually not too serious and that if you have a serious problem, the light will flash. If you can fix the problem for the $200 that your mechanic said it would cost, you should get it fixed. If this turns out to be a $1,000 problem, ignoring the check engine light might be the answer. My check engine light has been on for about 100,000 miles. I am not proud of it, but I can live with it for now.

I don’t know what the code was. He used his scanner, then called a mechanic friend for the interpretation. I’m just a bit puzzled about why the light went out on Tuesday, after being on for several days. I don’t think it had anything to do with the power failure we experienced here in South Florida that afternoon, but the timing was very suspicious (just kidding about the connection, really.)

Jeramy, I’ll support a man’s right to drive with his CEL on, but I don’t recommend it. Many things that trip a CEL can cause expensive engine damage if not addressed. Many can cause poor gas mileage. Many can cause other premature failures, like a cat converter.

I’m curious, do you know why yours is lit?

If this turns out to be a $1,000 problem, ignoring the check engine light might be the answer. My check engine light has been on for about 100,000 miles. I am not proud of it, but I can live with it for now.

Here in NH we just instituted Emission testing last year. The only testing we do is read the OBD. So a CEL light on would FAIL emissions. Also on some vehicles if the CEL light is on the car goes to a default mode. It may not drive like it should. It should be fixed. It’ll probably save you money in the long run.