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Topic: Check Engine Light not working................

in Forum: C3 Electrical


Check Engine Light not working................

Posted: 5/16/04 8:14pm Message 11 of 15
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CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
Posts: 6424
Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
I would have expected you to get the diagrams by now. If they don't show up by Tuesday, I will send another copy.

The info you have does start to narrow it down. This means the light circuit in the dash is okay. This brings us down to the light control module or the computer (ECM). The wire to the ALDL is the same that goes to the light controller, which in turn is controlled by the ECM. The diagram make it fairly clear.

Let me know when you get them, or if I need to send them again. Would you prefer a fax?


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Check Engine Light not working................

Posted: 5/17/04 12:54pm Message 12 of 15
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Brockport, NY - USA
Joined: 1/2/2003
Posts: 44
Vette(s): 1982 Collector Edition
Ken,
have recieved the diagrams. Where is the driver terminal.
Was going to check the computer connections.
There are a bunch of relays and some fuses behind the passengers seat and the computer is behind the drivers seat. Will keep checking and will keep in touch.

Thanks for the help so far..........
Dan. |cheers|


Check Engine Light not working................

Posted: 5/17/04 3:20pm Message 13 of 15
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CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
Posts: 6424
Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
Dan, look on the lower left part of the diagram. You will see a box labeled "check engine light driver module". When you grounded the terminal at the ALDL you grounded the yellow wire circuit 489. That's on the left side of the diagram. All the light driver does is supply a ground to that yellow wire. You will note there are only 4 wires on the light driver. In addition to the yellow, from the bottom left of the driver is a black ground wire. Make sure this is a good ground.

Do all of the following with the key turned on.
The colors I metion are the wire color, and are shown on the diagram. The circuit numbers are just on the diagram and are for reference.

Next look at the power input, a pink/black wire circuit 39 that get it's power from the gauge/transmission 20 amp fuse. This is shown at the top left of the diagram.

The last wire is the contol input wire, a white wire circuit 487. This is the signal the ECM (computer) uses to signal the light driver module to turn on the light. It should supply a ground to the light driver module. So if you ground the white wire with a jumper, the light should come on. If it does, the computer is not controlling the light, or there is a bad connection between the driver and the computer. You can check the wire by grounding it at the computer. Use the white computer connector pin G. at the computer.
If the light did not come on when you grounded the white wire, and the other three are good, the driver is bad.

Good Luck. Let me know.


Check Engine Light not working................

Posted: 5/17/04 6:32pm Message 14 of 15
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Brockport, NY - USA
Joined: 1/2/2003
Posts: 44
Vette(s): 1982 Collector Edition
Ken,
is the check engine module located in the same area that the ecm is located. On my 82 the computer is located behind the driver and passenger seats.
I have not found anything that looks like the ecm any other place.
Dan |cheers|


Check Engine Light not working................

Posted: 5/18/04 7:51am Message 15 of 15
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CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
Posts: 6424
Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
I hate to say it, but I'm not sure where it is on your car. It is ususally behind the dash cluster or in the console. It's not very big, and usually a plastic housing. I tried to find it on a parts locator and failed. I'll keep looking.


in Forum: C3 Electrical


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