When I let the fuel level get below about 10 gallons the gauge goes drops to zero and the ( Check fuel system message ) appears. After filling the tank everything returns to normal.

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What type of fuel are you using. Have seen this on another forum, and supposed cause is High sulfur gases (fouling the sending unit). I burn nothing but Sunoco or Shell 93octane in mine and have never had a problem. I never use grocery store, big box store or convenient store gas because you just don't know what you are getting. Not sure I should post a link to another forum, but there is a lot of discussion on it there.

I have a similar problem with my C5- the fuel gauge drops to "E" and the check gauge light comes on at about 7/8 and corrects itself when I hit about 3/4 of a tank.  This is a standard 350 ci, auto with 115000 miles. 

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