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1991 GMC 1500 Service Engine Light?

Tiny
FIREWLF771
  • MEMBER
  • 1991 GMC C1500
I have a 1991 GMC 1500 5.0 V8 that has 61,000 original miles on it. I bought it from an older gentleman the other month. The truck runs great. Since I bought it, I changed the spark plugs, muffler, catylic converter, battery, oil, transmission fluid, coolant, and brake fluid. The one problem is that the "service engine" light comes on ONLY when I've been driving at highway speed for over approx 15 mins. It won't come on if I'm doing city driving. Only highway. And the light will stay on until I shut the truck off. Why is this? Should I start carrying a fire extinguisher?
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Monday, September 17th, 2007 AT 7:21 AM

1 Reply

Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
If the truck runs ok and there are no noises other than normal noises The problem could be one of the sensors. I would Have the ecm scanned. That would tell you what sensor is making the engine light go on.
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Monday, September 17th, 2007 AT 8:32 AM

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