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What would cause a 9 mpg drop in mileage

I have a 2002 Honda accord and have seen mileage dropping over last several months. Car also feels slightly “doggy” but not enough you can ever quite put your finger on it. Tried to address by changing air filter and new plugs and wires. Check engine light has come on since tuneup and codes say could be oxygen sensor. Had new lower ball joints put on and rear bearings replaced as well as brakes.

Never had any problems with the car and the mileage has been rock solid at 31-32 MPG for 6 years. Two tanks of gas since the work and I am down to about 22 mpg.

Given your check engine light is on and the code says O2 sensor either have it diagnosed further or replace the 02 sensor(s) yourself. Quit guessing and get the CEL corrected.

A bad O2 sensor could cause this major drop in mileage. What are you waiting for…get it replaced.

I think it’s the extra drain on your alternator from the constantly lit check engine light. Remove that bulb and everything should be fine.



Get the car scanned and go from there. A leaking fuel pressure regulator could be the reason behind a recent loss of mileage.
Another possibility could be a slipping clutch or automatic transmission. If the latter, then there has been some problems with those. (A short cut and paste blurb below)

Transmission problems (2000, 2001, 2002): Automatic-transmission problems prompted Honda to extend warranty coverage to seven years/100,000 miles.