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  #1  
Old 03-07-2011, 05:45 AM
dcarrb dcarrb is offline
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Check Engine Light: A basic question

Shouldn't a check engine light stay illuminated until the offending code is cleared? What would cause the light to come on, then abruptly go out just a couple of miles down the road?

Okay, so that's actually two questions...

dcb
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  #2  
Old 03-07-2011, 07:27 AM
Stillhoff Stillhoff is offline
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Re: Check Engine Light: A basic question

Yes, if you have a foult.

A guess: the lambda.

http://www.subaru-svx.net/forum/showthread.php?t=54033

Last edited by Stillhoff; 03-07-2011 at 07:31 AM.
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Old 03-07-2011, 02:28 PM
Lookin4SVX Lookin4SVX is offline
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Re: Check Engine Light: A basic question

I have a CEL that comes on sometimes when I start up the car then goes off a little ways downt he road. When I pulled the code it was EGR issues.
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Old 03-07-2011, 02:44 PM
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b3lha b3lha is offline
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Re: Check Engine Light: A basic question

Here's the simplified version:

Each sensor is tested several times a second.

One bad result is usually ignored, but if you get several bad results in succession the ECU will decide there is a problem and trigger the light.

If you then get a whole load of good results without any bad ones then the ECU will decide the problem has gone away and turn the light off again.
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Old 03-08-2011, 05:54 AM
dcarrb dcarrb is offline
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Re: Check Engine Light: A basic question

Quote:
Originally Posted by b3lha View Post
Here's the simplified version:

Each sensor is tested several times a second.

One bad result is usually ignored, but if you get several bad results in succession the ECU will decide there is a problem and trigger the light.

If you then get a whole load of good results without any bad ones then the ECU will decide the problem has gone away and turn the light off again.
Thank you. I figured maybe it was the budget, no-name, 87 octane, petro-byproduct-laced "gasoline" with which I topped the tank before commencing a 2-hour highway run Sunday night that had my engine scratching its head. Haven't seen the CEL again.

dcb
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Old 03-08-2011, 09:50 AM
gbianchi gbianchi is offline
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Re: Check Engine Light: A basic question

Quote:
Originally Posted by Lookin4SVX View Post
I have a CEL that comes on sometimes when I start up the car then goes off a little ways downt he road. When I pulled the code it was EGR issues.
I also have had this cel situation, I believe it caused by old hard vacuum lines, always goes off though..........G.
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