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2004 SRX V6 AWD
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685 Posts
Discussion Starter #1
Per the warranty records, my 04 V6 had the converters replaced @ 15,000 miles with the original owner. Now @ 32,000 miles had another failure (indicated by P0420 codes) and both replaced by Cadillac dealer again on warranty - - luckily within the 8 yr emissions warranty period.

As best I can determine, there were no other system failures that would cause the converters to fail.

Any insight on what is happening here? I'm nervous about having to buy these on my own bucks in the future, although with no inspections here in Indiana I might be tempted to just drive on with the CEL illuminated.
 

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2009 SRX-4 Sport / TriCoatWhite
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1,185 Posts
Our SRX's run extremely RICH (Hence the lousy gas mileage for a V6)

So - - Rich fuel produces Rich pollutants, which eventually clog the pathways in the Cats, eventually causing them to overheat, eventually causing them to toss fail codes.

The newer cats have larger airflow ports, so it is less likely for them to clog / fail.

I'm lucky - - nearly 30k miles on the original set.

But don't ask me about timing chains. :)
 

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2007 SRX4 N*, 2004 Infinity G35 Coupe
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2,005 Posts
Prof/Nasc....I thought the same about the mixture. I would think the mixture selected by a manufacturer would be engine (requirement) specific for the best overall performance with a critical eye on engine operating temperature and the impact on fuel economy. No secret that auto makers are under the gun to improve vehicle and fleet fuel economy. And fuel economy "sells."

I was also tempted to observe it may not be the Caddy Cats or a subtle fuel-related issue that caused the emissions code failures we see on this forum. But a 15,000 mile failure and then again @ 32,000 miles----even with an 04 V6 (6+ model years, low mileage and hence low miles per year driven) also makes me think it is something else. That's driving only about 5,000 miles a year.

A DEPOSIT-CAUSED CLOG: I am wondering if the cat failure may be caused by the level of heat in the cats, or more specifically, a lack thereof. NASC....the low mileage on your 04 might suggest the cats don't get warmed up enough on a daily basis, long enough, each trip out, and the crud isn't being burned/heated off. The accumulation builds but never totally burns off. Over time, the crud builds, solidifies, and becomes even more resistant to burn off.

Even with the occasional 50-100 mile + trips. Then add in a colder, Winter climate driving in the mix, where the engine may be reaching operating temperatures. But is it long enough running at operating temps to adequately heat up the "catalyst" in the cats? By extension, I wonder if, for example, warmer climes SRXs don't see this Cat clogging issue, even with the low mileage ones, but the Northern snow-belt ones do.

CAT SCREEN FAILURE: The opposite of what I just posted may be true. The process of the catalytic convertor is simple. There is a screen in there coated with a catalyst (chemical) coating. The catalyst on the screen is supposed react to the the exhaust gasses, to heat up the catalyst to very high temperatures to burn off the deposits. While the catalytic convertor may be successfully burning off the deposits, the very high temperatures the screen is designed to create eventually cause the screen to deteriorate. The screen breaks down and then fails to allow the exhausr gasses to pass through the exit end of the cat. The deteriorated screen actually causes the exhaust clog, a back-up of the exhaust gasses.

Just a thought, a verbose one. What do I know.

I've had (only) one cat failure in any of my cat-equipped cars since the 1976 emmisions standard made cats mandatory. The "failure" car had both pre-cats AND cats. It was the pre-catalytic convertors that failed, both of them, left pipe and right, @ 78K miles. All 8 cars surpassed Nasc's 32,000 miles. Only 2 cars surpassed 100K miles. The average years of ownership 9. The average total miles per car 76K at retirement/trade/sale.

Maybe someone else has a clue here. Maybe I am raising more questions than I have provided insight. Sorry.
 

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2009 SRX-4 Sport / TriCoatWhite
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1,185 Posts
I am no expert on cats.. just a generalist.

I do know this. My best friend has a clunker he drives for work because he drives a lot. It is an old Buick Skyhalk 4 Cyl with 250k+ Miles on it. It ran great and then last month it started running like total crap. The more he drove it, the worst it ran. He brought it over to my house were we did plug, fuel filter, air filter, and replaced most of the Ignition parts. Still ran like crap.

I followed him home... and while doing so I noticed a strong RED Glow under his car - - the further we drove the brighter the glow got. By the time he got home he noticed the carpet on the passenger side of the car smoking! Wow! It was the Cat glowing like a freaking red lightbulb

Long story short - - took it to CarX and had the Cat replaced. He brought the old one home.. we cut it in half at my work on a band saw. Inside it was coated HEAVY with what appeared to be black suit. much of the honeycomb was clogged with the stuff. On side of the honeycomb looked burn and dried and crack and had crumbled upon itself.

Yes, Cats are supposed to get hot - - that is how they work.. but they are not supposed to get hot enough to melt their insides! :)

With the new cat on .. His car is once again running wonderfully. Better then it has in years according to him.

One thing - - if GM has SRX cat problems with 4's through 6's, but not the newer ones... then they changed something, I can only guess what. I recall discussions with mechanics regarding improved airflow through newer cats... .... I don't remember exactly who.

PJ :: I agree... you would think GM would try to tune for maximum MPG and performance... BUT.-My Audi Allroad got 19/28, my old Ford Explorer 4x4 got 17/21, and my SRX gets 13/19. Either there is something seriously wrong with my SRX engine, or GM did about the worlds worst engineering with it, or to get good performance they seriously sacrificed the MPG. Even my 05 Mustang GT with a modified 340rwhp V8 gets 17/28 and that is WITH me punching it and revving it every chance I get! Dealership tells me there is nothing wrong with my SRX engine - - so the latter must be the reason.

NASCAR :: Do keep us updated, I am most curious what you learn. If it happens again, I would consider an aftermarket Cat, rather then a GM Factory replacement that is exactly like the one that went bad the second time.
 

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2005 STS4 1SG: GM Acc Lights, Corsa, Platnium Grille, Volant
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15,987 Posts
My highly modded 98 SS gets 22 MPG average while my STS4 holds steady at 13
Performance has something to do with it but the major factor is weight, its a V6 trying to pull a heavy truck, simply put to do so itll stay in the upper RPMS to get it moving and thus use more fuel.

The only fuel advantage of the V6 over the N* V8 is not that of MPG but of the ability of the 6 to use regular while the N* required premium.
 
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