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Old 09-08-2013, 11:33 AM   #1
85_corvette
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Member Since: Sep 2013
Default 85 Corvette check engine light will not reset

Im at a loss here ive got a 1985 corvette with a check engine light that will not turn off I have connected A and B at the diagnostic port and gives no codes at all not even the code 12 system normal nothing tried this with three different jumper wires so sure its not a connection problem there. Anyways I have unhooked battery for several days positive and negative. As soon as hook battery back up the light is on. The car starts and runs great just don't understand why the check engine light is on??? Anyone that can shed some light on this that would be great im stumped.

Last edited by 85_corvette; 09-08-2013 at 11:35 AM.
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Old 09-09-2013, 12:34 AM   #2
Cliff Harris
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Location: Anaheim CA
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I'm not 100% sure because I have an '86, and your car uses a different ECM, but I see no reason why they would otherwise be different...

The SES light is connected directly to the ECM and goes nowhere else. That means that either the wire is shorted to ground or the ECM is bad. The way to find out would be to disconnect the ECM and see if the SES light goes out.

The RAM in the ECM that holds the error codes will lose all its data in a second or so. That means that you only need to disconnect the battery for a second to erase the error codes. You might have this connector on your car, which makes is MUCH easier to reset the ECM (on my car it is a short lead attached to the positive battery cable terminal):

Click the image to open in full size.
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Old 09-09-2013, 08:23 PM   #3
91tpiman
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Quote:
Originally Posted by 85_corvette View Post
Im at a loss here ive got a 1985 corvette with a check engine light that will not turn off I have connected A and B at the diagnostic port and gives no codes at all not even the code 12 system normal nothing tried this with three different jumper wires so sure its not a connection problem there. Anyways I have unhooked battery for several days positive and negative. As soon as hook battery back up the light is on. The car starts and runs great just don't understand why the check engine light is on??? Anyone that can shed some light on this that would be great im stumped.
If you have a solid CEL, then it is possible the chip could be bad too.
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Old 09-09-2013, 08:23 PM
 
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