Check engine codes - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-12-2007, 08:06 PM   #11
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Um, any ideas?
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Old 04-12-2007, 08:47 PM   #12
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Have you listened as Bill suggested to confirm where the noise is? The catalytic converter is the first large part of the exhaust system and will be roughly in the area of under the front seat. If the noise is coming from that area, it is likely the cat that is bad. Kicking it to see if it rattles could confirm that. If you're not sure of any of this, take the car to a muffler shop and they will be able to do a back pressure test to see if the cat is clogged.

The temperature gauges on the dash are not very accurate. How well does the heater for the car work in really cold weather? You could swap out the thermostat to see if that helps, as they aren't that expensive.

With the number of miles on your car, it'* quite possible that your oxygen sensor is at least tired. Bad gas mileage would be a good indication of a tired O2 sensor, and could be replaced and considered part of regular maintenance.
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Old 04-12-2007, 08:52 PM   #13
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IIRC the temp sensor for the gauge is not the same one the computer uses.
Someone correct me if I'm wrong please.
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Old 04-12-2007, 08:59 PM   #14
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I wasn't 100% sure, either but, I believe the '99s only had one sensor for both the gauge and the PCM.
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Old 04-12-2007, 09:07 PM   #15
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It could very well be that I'm thinking of one of my other vehicles...
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Old 04-12-2007, 10:59 PM   #16
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Default First things first...

Step one:
What I'd do first is replace the thermostat and crawl under the car while it is running to see where the extra-noisy truck-like exhaust note is emanating from.

And yes, the catalytic converter is the first big boxlike thing downstream from the engine.

On the other hand, instead of crawling under a running car, a safer alternative might be to just take it to an exhaust/muffler shop and let them find out the problem for you. Usually those places will put the car on a lift and point out the problem without charging you a diagnostic fee up front. Look for one that will give you a free diagnosis.

Step two:
Once those items are sorted and corrected, clear the codes and see if they come back.

But, then again, what do I know? I just paid over $1300 to get annoyed by a dealer service department... that story is in the Lounge.
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Old 04-18-2007, 06:26 PM   #17
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Thanks for all the help, everyone. By the way, the cat doesn't rattle whatsoever.. so I guess this points to me replacing the 02 sensor? And... is that fairly expensive? Or could I do it myself, maybe?
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Old 04-18-2007, 06:31 PM   #18
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If the cat rattles, it'* bad.
If it doesn't, it may or may not be bad.

Point being that it isn't ruled out, just not as likely.
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