Check engine light

WRIGHTEOUS87

MEMBER
1987 GMC SIERRA
V8
4WD
AUTOMATIC
300,000 MILES

87 GMC 1500, Check engine light will not come on when turned to on position. Circuit board is good, replaced all light bulbs. Won't pass smog because of this stupid light. Emissions are perfect though. Any idea. Could it be computer going bad? How do you test the computer (if possible). Can't get codes manually since light won't come on and have no access to a scanner.

4 Replies

MHPAUTOS

MECHANIC
31,937 POSTS

Best to get the ECU bench tested, most fault gathering systems will not work if the check light is not working, you may be able to plug in a known good test ECU to prove the theory.

Mark (mhpautos)

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Monday, November 22nd, 2010 AT 1:09 AM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

An 87 doesn't use a scanner. They have the plug that you jump to make the "CHECK ENGINE" light flash codes. Isn't that ironic. The only thing I can tell you is to follow the wiring back from the light to the PCM to see if there is a break in the wiring.

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Monday, November 22nd, 2010 AT 1:09 AM

WRIGHTEOUS87

MEMBER
3 POSTS

Thanks guys. I was also wondering if you have ever heard of a "fuse" in the wiring from the light to the ECU. A buddy put the same 87 350 set up in his off road jeep and said there was this tinny little PITA fuse that was causing it to stall (which mine is doing) but I don't believe nor see it in the Chilton book. His was aftermarket so I'm betting it didn't come stock since I can't seem to see it anywhere. Thanks for the help.

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Monday, November 22nd, 2010 AT 5:28 AM

JACOBANDNICKOLAS