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Worst Gas Mileage after battery change


I have a 2001 Hyundai Sonata. I change the car batter myself. After change the battery I drove like 50KM. I notice I got the worst gas mileage ever. Now it’s getting an average like 2-3Km from a petrol liter. I got an average 10Km from a petrol liter. Is there any reset I should have done after putting a new battery?

Thank you.

No, you DID the reset by replacing the battery… I suspect you are using the car’s mileage calculations to determine your fuel use. THAT is what got reset and it takes a little while to properly update the actual mileage. It also resets the “learned” values for the engine and that can reduce mileage for a little bit until the cars computer “learns” your engine again.

You don’t need to do anything but be patient.


Do you not reset the read out each time you fill the fuel tank . Changing the battery does the same thing . You need to reset the ( MPG-AVG speed - Trip Odometer ) and that will give you a better idea of your actual fuel usage for the type of driving you did on each time.

Also check your fuel usage the old fashioned way once in a while to see just how accurate the read outs are.

Is your check-engine light on? Does your car smell like gas (petrol) or rotten eggs after you drive it?

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You could have knocked out some other parts while doing the battery change.Did you remove anything else that was in the way to take out the battery? On mine I have to remove parts of the airbox assembly to gain access to the battery