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Old 11-11-2018, 05:15 PM   #1
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Join Date: Mar 2007
Location: los angeles
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CATS - do they go bad?

I got a CEL on my 986 S. I hooked up my durametric and got the code but don't remember it right now. I looked up the code which basically said a CAT isn't doing anything. There weren't codes for the O2 sensors. There are 70k miles on the car. The front O2 sensors have 30k miles on them and the rears maybe 10k miles. The CATs have had an easy life - no AOS or IMS blowouts. So, would a CAT really go bad with so few miles?

I collected front /rear O2 sensor output data and put it excel, but that only added to the confusion. The signals rapidly oscillate. There needs to be a way to average the signal over time.
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Old 11-11-2018, 06:12 PM   #2
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Cats can go bad.

I don't recall the exact procedure but I believe you can check their performance by using the Durametric to look at the before and after O2 sensors and can compare their profiles.

If I recall correctly, the rear profile should look essentially flat compared to the front's wavy line. If the rear looks like the front sensor's profile, then the Cat isn't doing its job. Of course this assumes, the O2 sensors are working correctly.

Others can confirm is my recollection is close or not. Hope this helps.
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'01S 986 (Sold after 16 years ownership)
'78 924 (carburated; sold when moving to CA)
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