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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 03-15-2007, 09:38 PM   #1
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Default Check engine codes

My check engine light came on about a week ago. How do you find out what the code is?
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Old 03-15-2007, 09:41 PM   #2
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The only way is with a code reader, or a scanner. Take it to Autozone or Advance and they should be able to get the code for you.
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Old 03-15-2007, 11:29 PM   #3
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Thanks!
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Old 03-16-2007, 08:10 AM   #4
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Then.. w/o needing to say it. You'll come back here and look up the codes in Techinfo and we'll help you fix the problems.
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Old 04-07-2007, 04:42 PM   #5
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Well, I finally got around to going to Autozone to get the code, and it issssss

DTC P0420 Catalyst System Low Efficiency

The guy said it could be a clogged catalytic converter, something with the O2 sensor... but he did say that it could be a number of things with this code. Anything that would be really typical for a Bonneville? I seem to read a lot about O2 sensors...

Oh, and if it helps, the only thing funny I've noticed about the way it runs is that it'* REALLY noisy, kind of like a truck and it seems to be coming from the back end, like around the exhaust or something. Other than that, it seems to run normally...
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Old 04-08-2007, 11:53 PM   #6
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I'd have you lay down next to the car while it'* running to see if the noise is really by the back..or by the catalytic. Sometimes a hole will actually blow out the side of the catalytic when they go bad.

IIRC Haro posted this about his 95 back in the day.
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Old 04-09-2007, 07:35 AM   #7
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Kick your cat. Up and down, side to side. Hear a rattle?
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Old 04-09-2007, 09:41 AM   #8
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He means the one on the car Rach...lol

It'* possible the cat is clogged/bad.
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Old 04-09-2007, 05:19 PM   #9
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I found out more things, I think.

My temp gauge always says like, 160 instead of being close to 200, which I know is wrong. I asked my uncle about it, and he said that would explain why the catalytic converter was clogged, because the thermostat is telling the computer the engine'* colder than it is, so all kinds of extra fuel is getting pumped... and... I think that'* about it. So, does this mean I need a new thermostat, and catalytic converter? He also said I'd probably need a new 02 sensor, why would that be?

Also, for the kicking part (ha), is the cat that big box thing under the car?
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Old 04-09-2007, 05:21 PM   #10
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Oh, and I guess what I'm also asking is, could this all be related to a bad t-stat? It seems like that would be the root of everything. I'm getting terrible gas mileage too, I'm assuming that'* cause my car is using way more fuel than it needs to.
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