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During my last road trip I encountered the weirdest issue with my 2011 Hyundai Accent. On the highway the RPMs went down to 0 but I was able to drive completely normal. After I turned the car off, I wasn't able to start it back up again. Only after about 45 min of cooldown, the car started and everything went back to normal. After about 30 min driving I noticed a little stutter but everything seemed normal. But the moment I started braking enough (potentially downshift) the RPMs went back to 0 and the same issue repeated itself.

I brought the car to a nearby mechanic and they couldn't find any error codes. They didn't really try much else since it was Saturday and they were about to close.

I'm thinking maybe a faulty sensor. Maybe related to some heat expansion. The only weird thing is that I'm able to drive for ages with the revs normal as long as I'm not breaking. I managed more than 30 min on the highway on my drive back home. But the second I break a little the whole story happens again.

Any ideas are highly welcome!

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  • Welcome to Motor Vehicle Maintenance & Repair! You state, "After I turned the car off, I wasn't able to start it back up again." Do you mean you'd turn the key, the engine would rotate over, and the engine wouldn't start? Or do you mean, the engine itself wouldn't turn over on key turn? You turn the key and the dash lights up along with the gauges?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 16, 2023 at 10:51
  • Yeah exactly, the battery and all that were fine. We stopped at a gas station and we tried to jump start the car and that didn't go well either. It just kept doing this start noise but without managing to get the engine going.
    – Mr.Floppy
    Commented Aug 16, 2023 at 16:42

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It is most likely a faulty crankshaft position sensor. This sensor tracks your engine r.p.m. That's why your tach goes to 0. On many cars when they fail while running the computer remembers where the engine is at and continues to run. Once you shut it off, it doesn't know how to time the engine and it won't start. But it will crank. Heat oftentimes will cause a faulty sensor to fail. That's why when it cools down it starts working again. These sensors very often do not throw a code when they fail. I am a little surprised that it didn't throw a code when you can drive it with 0 r.p.m.s on the tach. At any rate a good mechanic will find this. He may even just replace the sensor because they are inexpensive and usually easy to access. It is easy enough that if your a little mechanically inclined, you could do it yourself.

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  • Thank you so much! I will probably looking into fixing it myself first but might just push the information forward to the mechanic. I'll let you know if it was that :)
    – Mr.Floppy
    Commented Aug 16, 2023 at 17:01
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    This seems highly likely to be the culprit.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 16, 2023 at 17:35
  • I can confirm, this was the issue. Thank you so so much!!! Paid 20 bucks for the part and spend not even 30 min to swap it. Now she runs perfectly fine again :)
    – Mr.Floppy
    Commented Sep 8, 2023 at 3:01

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