I have a 2012 Kia Sorento that has lost its strength/power when getting up to highway speeds (65 mpg highway speeds here in CA. it struggles to do it. It doesn’t stop wanting to move forward though) and while going up hills. Once it gets up to speed it doesn’t kick into the next gear like it should all the time. It will just rev high until I take my foot off the gas and then it will change gears. Also my average gas mileage was about 20 MPG but it’s gone down to about 12 mpg on average. There was this one day where the average started at 10 mpg and then shot up to 30 mpg (which I have never seen it do before ever), seemed to drive fine (I didn’t push it though) and gradually dropped back down to about 20 (my normal average). The next time I drove it it went back down to averaging about 12 mpg again. All this has progressed over about a months time.

I took it to a local garage where they charge $200 for a diagnostic. I had them do it and they called me back saying there were no codes when they checked and they had used all their diagnostic time and would have to charge me for another diagnostic (so another $200) to keep looking for the issue. They thought it was a blockage of some sort in the exhaust. They ran a camera up there I guess and didn’t see anything though. I declined the second diagnostic ($400 to just diagnose the issue without finding a fix seemed to be a bit much). I’m getting ready to take it to a dealership since it has a recall on it for possible metal shards in the engine. Also they want me to bring it in for a software update.

It almost seems like it’s in “Limp Home Mode” but no lights are on (no check engine light or anything on at all”.

Any thought or idea’s? I’m worried this will turn into a money pit. I would super appreciate any input or things to ask the garage to check for.

  • Hi and welcome. Have you been measuring MPG the (accurate) way of filling the tank and using the odometer (or trip odometer), or are you relying on a dashboard gauge?
    – mike65535
    Dec 18, 2018 at 21:10
  • I’ve just been using the dash average.
    – Lacy2
    Dec 18, 2018 at 21:13
  • The dashboard gauge sort of guesstimates the MPGs, using various sensors in the car (fuel flow, engine speed, manifold vacuum). Since you are experiencing a drivability problem it could be that a vacuum hose has worked it way loose. Was any work done on the car in the weeks prior to the problem appearing? Oil change. etc.?
    – mike65535
    Dec 18, 2018 at 21:19
  • No work done. I did have an oil change done after all the symptoms had started and been happening for a week or so in hopes it would help. But it didn’t. All the symptoms were still happening so an oil change didn’t help or make it worse. It remained the same.
    – Lacy2
    Dec 18, 2018 at 21:36

1 Answer 1


This sounds like a transmission issue to me; The first thing I would check is do you have enough transmission fluid?

You can dismiss the gas mileage issue as it's likely due to your car spending egregious amounts of time in the wrong gear - You mentioned it's not shifting at appropriate times.

My car experiences similar issues when I get about a half quart or so low on transmission fluid..... Check your levels, if they're a bit low, add a half quart and check again... keep going until they're in normal range.

If that ends up being true, wait a few days / drive a bit for a few days and see if it helps.

Otherwise, see if you can find a transmission specialist that can look at it? Someone that focuses on that kind of work, not the pepboys/[Insert name of other generic place here] down the street

  • My husband said he thought it was a transmission thing too but the garage didn’t say anything about it. The garage I took it took it to said they checked all the fluids though and said everything was fine. 🤷‍♀️
    – Lacy2
    Dec 19, 2018 at 2:55

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