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Q: bad gas milage on 2002 Chevrolet Silverado 1500

Enthusiast 01be16a5a93688912f14755221fb15211b518d9a788cf01b455e03cc1bd585ac
it went from getting 18 to 19 mpg. down to around 12 mpg. has anybody had this happen and found what caused it?
(2) Answers
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Assuming you are checking your mileage at highway driveing it could be several differant things that could cause a decline. A lazy O2 sensor or a coolant thermostat that is staying open causing engine temp to run lower are things I look at first. Air filter or dirty mass air sensor can cause low fuel mileage. Of couse the basics should be checked first but cannot rule out a brake caliper draging or transmission that may not going into overdrive. Im sure someone else will comment on things I have failed to mention.