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Catalytic Converter issues

I had my Catalytic Converter replaced in my 1999 Suburban in April 2008 because, according to my mechanic, the Check Engine light code said that is what was needed.

Now it is December 2008 and I have driven my Suburban only 4000 miles and the Check Engine light is on again, and the mechanic says it is the catalytic converter again. They checked everything they can think of that would make a catalytic converter go bad, and everything checks out OK.

The mechanic does not want to replace the catalytic converter under warranty (2 years or 25000 miles) but wants me to pay again, which is quite pricey.

Two questions for you

1) What would cause a catalytic converter to go out so soon?

2) Any suggestions as to what I can do to get the mechanic to cover this under the warranty of the part?

I would take the car to another mechanic to have the fault checked without mentioning the catalytic converter situation at all.

What is wrong with it could be the mechanic himself trying to make an extra Christmas buck. I am nasty enough to think that maybe the original converter was not replaced.

Again, pay another mechanic to trouble shoot the why the light is coming on.

In order for the mechanic to reject your warranty claim he must come up with some maintiance or repair issue that you ignored and that neglect caused the cat to fail early,is he claiming you ignored some issue?

Is it possible that your vehicle burns oil and/or has a head gasket issue? If the engine is burning oil or is passing antifreeze/coolant through the cat converter, that could cause it to fail.

I had that checked and the mechanic says that none of that is happening. Is there a way I can check myself for oil/antifreeze/coolant issues in the converter?

Now the mechanic is admitting that he doesn’t know what is wrong. The code did not tell him to change the catalytic converter the first time. He may have been correct to change it but he didn’t know then and he doesn’t know now. He will charge you for the new one and then make the claim for the bad converter anyway. He will make quite a profit on your car. If you have the paperwork on the part, any other shop can do the work if they are a dealer for that part and even if they are not. Shop this job around a bit. A cat will quit if there is too much fuel that goes into it (without being fully burned). Too much burning oil is another one. Defective cat.

How about getting the actural code (Like P0123). It would help greatly. Codes, report what sensors tell them They don’t say replace the converter, they say things like xyz has been detected. xyz may be an indication of a possible converter problem, but it also could be something else or a bad sensor.

This Is And Isn’t Rocket Science

Similar catalytic convertor problems come up here quite often. Here’ one from just a week or so back. I hope HelloKit doesn’t mind my posting his response to this question:

Toyota Tacoma Engine Light
I recently bought a 2001 toyota Tacoma from a chevrolet dealership and the night I bought it the engine light came on. i took it back the next day and they scanned the computer code and told me the oxygen sensor needed to be replaced. since they had replaced the catalytic converter at a nearby toyota dealership under warranty before i bought the car, they would find out if the oxygen sensor was under warranty and if not they would replace it themselves- which they did. the next day the engine light came on again so it took it back and they said the other oxygen sensor needed to be repalced which they did. the next day the engine light came on again and i called them and they told me they had no idea what was wrong and they set up an appointment at the nearby toyota dealership who had replaced the catalytic converter. they said the computer was broken and so they replaced it. the next day the engine light came on again and so i called the chevrolet dealer ship who said to take it back to the toyota dealership to diagnose it and after 6 hours they said they had no idea what was wrong with the car but it might be the gasoline. the next day the light came back on again but it went off the next time i re-fueled then came back on again. is this car a lemon or is the check engine light not a big deal? is there something wrong with the truck they should be able to find and fix?

Here’s what HelloKit had to say about this problem, recently.
Much of this problem has been caused by Toyota Motor Car Company, parts suppliers, and parts catalogers, and, then, ignorance on the part of would-be repairers. Ignorance is curable. The other stuff…I don’t know.
I’m not trying to be factious by saying that the Chevrolet dealer should farm this job out to the Toyota dealership. The Chevrolet dealer has, already, sunk a number of expensive parts into it, haven’t they? Farming it out could, actually, save them money,as compared to throwing more parts at it, right?
At the crux, I think, is the matter of getting the correct part to install. Late model Toyotas, at least some, use what is called (either) a wide-band oxygen sensor, or (the exact same thing) an A/F Sensor (Air/Fuel). The “wide-band” oxygen sensor may be used in the front of the catalytic converter. It may, or may not, be used in the back of the catalytic converter. A regular oxygen sensor (“narrow-band”) may, or, may not, be used there. (See how simple it is?).
To further complicate matters (Thanks, whomever!), the criteria for getting the correct part depends on: 1. Is it a 4 cylinder, or a 6 cylinder? 2. Does it have an automatic transmission, or a manual transmission? 3. Is it an extended cab, or not? 4. Does it have California emissions package, or Federal emissions package? 5. And, of course, is it the front (of catalytic converter) sensor, or the rear (of the catalytic converter) sensor?
Vehicles which use A/F Sensors, use very different parts than those with “regular” oxygen sensors; but, they don’t appear to be that different. The catalytic converters are different, the engine computer, and other stuff are different.
Oh! Not all mechanics, or service people, know this stuff. A shame. You could download, and print, this little note for them.
Here’s a link to a parts supplier. It shows some of the things which can cause this confusion. The two brands, Bosch and Denso, are both reputable brands. It’s just that Denso is about twice the price of Bosch. http://www…ultSet.htm

ADDED: Diagnostic Trouble Code (DTC) P0420, “Catalyst system below threshold (bank 1)”, can be caused by the wrong type of parts (wide-band, or narrow band oxygen sensors), etc.,being in place. In short, it needs troubleshooting by an adequate mechanic,with adequate tools, and adequate knowledge.
Updated: 11/24/2008 10:10:50 AM

As Joseph Meehan has advised, post the code(s) here. Maybe someone can give more advice.

Don’t be confused by that post about a Toyota with wide band oxygen sensors. Your suv has the commoner narrow band oxygen sensors; so, that’s not an issue.
What is an issue with your suv is the quality of the troubleshooting and the resultant questionable quality of the repairs.
Here is a short checklist of what the mechanic should look at when a code comes up for the catalytic converter:

Hello Kit, Thanks For Correcting Me. Sorry About The Confusion. Thanks For Reponding.

These catalyst deficient problems can also be confusing and misleading to many mechanics.

I am still dealing with the 2001 Toyota Tacoma engine light issue but I wanted to offer another idea for finding out what is wrong with your car- Toyota has a forum for Toyota users called Perhaps your vehicle manufacturer has the same thing like this Community Forum electronic bulletin board on Car Talk? Good luck!

The actual code is P0420 as you stated above.

After further discussion with my mechanic and going over the list provided he responsed that the O2 sensor was operating normally according to the tests that he provided. I have not put leaded fuel in the suburban to my knowledge. The timing is OK. The coolant temperature appears to be operating with the normal values, and no leak is detected. The exhaust system does not appear to have a leak.

I am wondering if you can elaborate a little on the one that says “The oxygen sensors in front and behind the converter are reporting too similar of readings” What is too similar? What should normal readings be?

If I ever find out the cause of the problem, am I still going to have to change the catalytic converter or is it still good? Is there any way to rule out the converter and test it without relying on computer codes?

A more direct test of the catalytic converter would be with an exhaust gas analyser looking at the exhaust gases at the tail pipe. If the gases are what they should be, the catalytic converter would be good.
The usual test of the efficiency of the catalytic converter is somewhat indirect. The signals from the front and the rear oxygen sensors are looked at on a scan tool, or oscilloscope. If the front oxygen sensor signal has large swings, and the rear oxygen sensor signal has small swings, it’s assumed that the catalytic converter is operating correctly. This relies on both oxygen sensors being correct.

Some cars have 2 cats- is that what your mechanic is saying- that it’s the other cat that’s bad? Other wise, why wouldnt you be eligible to have it replaced under warranty- did he use aftermarket parts? another thing my toyota dealership tried was to replace the cpm- but it could be just about anything- did you look at it has a long list for troubleshooting the code that is very thorough.