02 seville sts strange sound revving

[mywifests]

my 02 seville sts i just got makes a rattling sound while revving, sounds like its coming from directly under the front seats section of the car, i'm pretty sure it's something to do with the catalyc converter. i'm new to this forum. any suggestions?

[Cadillac Jim]

The catalytic converter consists of a case with a ceramic core mounted in it. The ceramic core has many small tubes through it that the exhaust flows through. The insides of the tubes have a very thin coating of catalyst (platinum, palladium) that causes unburnt hydrocarbons and carbon monoxide to light off with the oxygen in the exhaust, much as do the catalytic pocket warmers and lighters you can get at sporting goods stores.

If the ceramic cracks, as it can do if you high-center, or if stress on the system loosens the mounting of the ceramic and vibration gets to it, then you get a rattle. That is probably what you are hearing now. This breaks off small pieces and some of them get blown back into the mufflers, clogging them. As the cracking and fragmentation progresses, the cat and then the mufflers slowly clog up. The engine is affected as this progresses. First, you will notice that the torque curves moves toward the lower RPMs and the gas mileage goes down a little; around town all you may notice is that it actually seems to run a little better, at the expense of entrance ramp and passing power on the freeway or highway. Then torque slowly decreases across the power band but is worst at higher RPM and the gas mileage goes through the floor. Eventually the car will barely move.

You can verify that the noise is the catalytic converter rattling, not just a rattling heat shield or broken clamp or motor support, by holding a long rod such as a broomstick against the cat and holding your ear against it while the car is idling.

If you catch it quickly you can replace just the catalytic converter. For some reason dealers of all makes are very expensive for catalytic converters. I would suggest that you go to Midas or any other reputable dealer that does a lot of stainless steel exhaust systems; it will be a little under $200 there. Be sure that if they weld anything (this is quite likely if they need to replace the mufflers too) that they use stainless steel mufflers, pipe and welding rod, otherwise the welds will rust in a few years and break. You have a million-mile exhaust system, and don't let anyone talk you into giving that up for their personal convenience.

[mywifests]

thanks jim, that helps a lot. Also, if im not mistaken i think the cat is covered under warranty until 130, 000km or 96 months. It says in the car's GM service records under "Applicable Warranties": 96/130000 FEDERAL EMISSION CATALYTIC CONV. effective date 08/21/02 end date 08/21/2010. Does that mean the catalytic converter could be fixed/replaced by the dealer under warranty?

another question also.. i just spotted something strange looking at the service records. the VIN of the car is 1G6KY54992U305986 and it says merchandising model: 6KY69-2002 Seville STS, BUT

on the AUTO CHECK Accident Reporting System it says

VIN: same as above

VIN Decodes as: 2002 Cadillac Seville SLS 4D "SLS????"

VIN Accuracy: Decodes Correctly

Accident History: No Activity Reported

The car was listed as Seville STS by the dealer, the car has the STS emblem at the back, the GM service records indicate it as being an STS???? so im confused.... someone told me about the 5th digit of the VIN , if its a Y its an SLS, if its a 9 its a STS, that's where the Y and 9 engine codes fall in the VIN number. I don't know if this is true or not.. could this be a major error? Is there any way of finding out if I have the STS engine or the SLS engine? please help.

[Logan]

Could be the Cat heat panel barking at you..

IF it was a bad Cat. I would expect some post cat codes..

I'am seeing 160km numbers in this post?

Canada?

I dont think US regs will fly in Canada. Currenty US FED regs are 8 years on the pcm and the cat.

[Cadillac Jim]

The VIN number checks out as an STS (KY as the 4th and 5th digits, 9 as the 9th) and the VIN check digit (the 8th) is good. The model year is 2, which I believe is 2 but I don't have hard information on the VIN model year code for 2002.

Logan has a very good point: run the codes and post them; a cat can obstruct without throwing codes but if the efficiency is affected you will get something like P0420. This code is

P0420 Catalyst System Low Efficiency

Here's how to run the codes:

http://www.caddyinfo.com/readingcodes.html