Mailbag: ESV CATS dying

[Bruce Nunnally]

Hello Bruce, I was looking for instructions on starting a post/thread but can’t find it. I’m having trouble with my 09 Escalade ESV and was wondering if anyone else had ever encountered my problem. In November the check engine light told me I needed to replace the oxygen censors. In December it came on again and said my Catalytic converter was bad so I had them replaced. In january the light came on again and it was the CATS once again, they told me I must have got a defective set and replaced it for free. Now its february and once again the trouble code is telling me that catalytic converts are bad. Any idea what could cause the catalytic converters go out every (1)thousand miles on average? Now I am being told that the only way to find out is to tear the engine down ($1,500) and then fix whatever they happen to find… FOr the record I have about 114k miles on it now and these are the first real problems I have ever had with it.

[Bruce Nunnally]

The cats can go out if the engine is running too rich. The engine can run too rich if the O2 sensor is bad. However, your Dealer should be able to run a clear diagnostic that shows if the car is running in the right fuel ratio range; I am surprised someone would suggest the engine has to be torn down to diagnose this.

[Cadillac Jim]

Bad gas, such as filling up with off-road leaded gas at a contractor site, or perhaps in some overseas locations, can cause a cat or oxygen sensor to fail. It takes more than one tank. Some industrial fuel intended for off-road equipment, aircraft, or racing isn't intended for use in cars and won't really work in them. Other things, such as use of 85% alcohol fuel in a car designed for not more than 15% alcohol can damage the fuel or exhaust system. Putting a little engine oil designated for Diesel engines in a gasoline-burning car that burns a lot of oil can damage a cat or oxygen sensors because the oil has different additives. Running out some diesel fuel put in the tank by mistake can cause damage; I suspect that it's similar to damage caused by heavy oil burning.

I have had a few catalytic converters go bad in a short time after installation. They were dropped in storage or shipping and had a cracked element. Something that can do it in a car is high-centering on a bad driveway or curb and hitting the cat, or other impact under the car that hits the cat and cracks the element. The cat will gradually go bad, and usually will have a rattle that gets steadily worse.

It seems like your mechanic is at the give-up stage and wants to rebuild your engine, which I really doubt is going to fix anything. As Bruce says, there is no evidence that anything beyond the dash messages is being looked at. If you are sure of the car and the place that you buy gas and oil, I would have it looked at by a GM dealer that has techs with better training.