Help with 2004 Chevy Trailblazer engine light and ticking?

  • Thread starter Thread starter S.W.
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S.W.

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My 2004 Chevy Trailblazer's service engine light will come on if my gas tank gets low, if I have just filled it up, and if the weather/temperature changes significantly. Seriously. Tightening the gas cap usually makes the light go off, but this time it is stuck on. The truck runs fine - no problems. Any idea what is causing this? I know that there is some kind of emissions meter that is affected by this. Also, there is a medium-loud tapping coming fro the passenger-side rear of the truck. It goes off after a minute or two. Again - everything runs well. Any idea what's causing this???
 
Not sure on the tapping noise. I would replace the gas cap the most common reason for the check engine light is a gas cap leak.
 
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