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  1. #1

    Angry Gas mileage-performance

    I have recently purchased a 2005 Silverado 2500HD 2WD 6.0 Liter with very low miles. I had a bad oxygen sensor and replaced it. I unhooked the battery cable to reset computer but after running several tanks of gasoline through the vehicle, I still only get 9 MPG! The vehicle may have been recked even though carfax doesn't reveal anything.I thinking that something is a little off here!I have a 2002 2500HD 4WD 6.0 liter that gets 14-15 MPG! Please help I would like to know if something needs to be reset and or adjusted.

  2. #2


    With that low mpg, it would pay you to take it to the dealer to see if the computer needs to be re-set or what ever they can do. You don't expect "great" mileage with that truck, but 9 is ridiculous. Good luck!

    2010 Z/71 Colorado C/C
    Black 4X4 w/5.3L V8
    2007 Winnebago Adventurer
    w/8.1L Chevy & Allison 6spd.
    Canyon Lake, Texas

  3. #3


    In these situations, is the dealer merely re-flashing a new progam on the ECU...i.e. has someone previously put a different program on the ECU that's causing the poor mileage that the new owner doesn't know about?

    I've got a 2002 that's only getting 11-13mpg, which doesn't seem very good to me, and I'm now wondering if maybe the PO did something that the dealership didn't know about/disclose?


  4. #4


    more than anything, the dealership is just resetting all the values for various settings that the motor has set to factory values. What happens with the computers in vehicles is that they have a set of values that it runs off of to determine when to do everything. Now, these values can greatly affect mileage and performance. However, different people and different data coming from sensors can cause the computer to decide to alter the settings to optimize performance. So, it "learns" the driving habits of the driver and motor. If the vehicle changes hands or gets very odd reading from sensors, it won't know what to do since it's not used to it. So, you reset the computer back to factory default, and it can learn about the driver's habits and sensor readings it should expect. I would think (but can't garuntee) that if there were a newer version of the firmware the computer uses that the dealership would update it for you, since it probably has some fixes to better fuel mileage or fix running issues. There isn't always an update, but there could be...

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 277K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half

    There are 10 kinds of people, those who understand binary, and those who dont...

    Remember kids, the only difference between screwing around and science is writing it down- Adam Savage

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