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I've owned two vehicles whose catalytic converters were recalled due two a couple of reasons: one being the quality of the CC and the other being a reduction in power due to a material building up and reducing airflow.

The car I own now (2007 Pontiac G6) has had such a recall issued, but only some cars are affected. I feel that sometimes I have less power than I'm supposed to have.

Are there tests for bad CCs? My exhaust pipe is welded on to each end of the CC on the G6 so I can't exactly peek inside.

Thanks!

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How many miles does it have on it? –  Mark Johnson Apr 2 '12 at 14:05
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  • If the cat rattles (may happen more after warmed up), then it's definitely bad. Banging on it can help see if there is material loose in there.
  • If the cat was plugged up enough to affect performance, I would hope that one of the 02 sensors would kick off the check engine light. However, if it's borderline, I guess the engine may be able to adjust the fuel levels enough to make itself happy without adjusting enough to trip the CEL.
  • To really and truly know, you'd have to check the back pressure ahead of the cat and compare it against factory specs. I've never had to actually do that though. Anytime I've had a cat plugged so bad that it affected performance, it caused the vehicle to outright misfire.

All that being said, "I feel that sometimes I have less power than I'm supposed to have" is a really broad statement. Most things that affect performance on a modern car (enough to be noticeable) should trip the Check Engine Light and give you a place to begin troubleshooting.

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There's only two things that have me a bit perplexed: I'm getting poor gas mileage (about 4 mpg less on the freeway, which I might be able to attribute to the colder weather), and once in a while when I shut the car off it continues for another revolution and sputters for about a half of another (usually only after really short drives). Maybe I should just have it looked at... –  Cory Larson Mar 8 '11 at 12:23
    
It may just need some regular maintenance (such as spark plugs), or something may be malfunctioning. If something is actually malfunctioning, it will take an experienced technician and specialized tools to properly diagnose. –  S_Niles Mar 8 '11 at 18:10
    
Plugs on a 2006 G6 are good for 100,000 miles. If they go bad ahead of that, that's just a symptom, the real problem is somewhere else. –  Mark Johnson Apr 2 '12 at 14:06
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