Hyundai Sonata Check Engine Light On Transmission Shifts Hard

Reader Question: I have a 2001 Hyundai Sonata with 152,000. I have had regular maintenance done on it at every 15,000/30,000/45,000, etc. miles.

Currently when I drive it when it shifts (automatic transmission V6) around the 25MPH point it shifts rather hard unless when just above 25 MPH I let up off the gas to allow easier shift.

When it does make the hard shift, the Check Engine Light will come on and the car seems like it is driving in the wrong gear (I guess) but it will drive.

A friend put the hand held computer on it and the code shows I need a speed sensor. Is that enough or do you think I am looking at transmission problems? Is there a code when it is the transmission?

Thank you for your advise.


Hey Jeannie,

I really need a little more information and would like to run some tests myself to really be sure what is happening here but if you have a speed sensor code that is showing up in the computer memory, I would look into that code more and test the sensor.

This could very well be a bad speed sensor problem or there could be something wrong internally with the transmission. You do have many miles on this vehicle, so internal transmission wear would not surprise me at this mileage point.

Before you do anymore than replace the speed sensor, I would get a reputable transmission shop or even the Hyundai dealership to diagnose this problem further. Your regular mechanic is probably not the best guy to troubleshoot an electronic automatic transmission problem.

If the transmission is deemed to be the culprit, get 3 estimates from local transmission shops for a complete overhaul. You might not need a complete overhaul for this problem but at this mileage, I would be prepared to overhaul it once they disassemble it and do some inspections.

You do not want to be sticker shocked if they later determine an overhaul is needed.

Austin Davis

35 Comments on "Hyundai Sonata Check Engine Light On Transmission Shifts Hard"

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  2. Wale says:

    Just bought a hyundai sonata 2001 model. I really like the car and it drives smooth. Now the transmission wont engage into any gear. Car wont drive or reverse. please help.

    • By Austin Davis says:

      Well, my first thought would be is the gear shifter actually connected to the transmission or did something external break or wear out so the linkage from the shifter inside the vehicle not connecting to the transmission? If the linkage is still intact, is there transmission fluid inside the transmission, or is there a leak and the fluid is too low? If linkage is ok, and fluid is FULL, then I can only assume there is an internal transmission issue that will require a transmission shop to inspect. If this is a stick shift transmission you might need a new clutch, which will still require removing the transmission and replacing internal parts…..clutch disc, pressure plate and release bearing.

  3. Ben says:

    I had error code p720 on my 1999 Hyundai Sonata. I replaced the speed output sensor but I still have the code and the jerky transmission. Could it be the TCM?

    • Austin says:

      Hey there, not sure if you read or posted this, but I found it while doing some research for you.

      The code you got is pretty clear, and replacing the sensor is what I would have recommended, I am not a transmission mechanic and dont have any personal knowledge with this code on this vehicle. I did not see any technical bulletins about it either. I can only really suggest you have a transmission shop rescan your code and give their input. it would be a cheaper solution than buying a TCM as a guess 🙂 Although, you might call a junk yard in your area and see how much as used one costs, it might be cheaper than I think used.

      Sorry I cant help more

  4. Stephanie says:

    Hey guys, I’m back! Lol. I had to get my transmission range switch fixed at the dealership and now my car is going through all the gears fine. It cost me $225 (parts, labor, and taxes) to have that taken care of. Now I have to fix my mass air flow sensor because my car is idling around 500 rpms and it’s been stalling a lot after I turn it on.

  5. Stephanie says:

    I went to AutoZone today and got my codes read. I’ve got a P0171 (fuel system too lean) and a P0706 (open in transmission range switch). Any ideas?

    • Austin says:

      It’s like me taking your blood pressure, I can tell you that it is too high….but I have no idea why or what you should do, except go see a real doctor. Same thing with places like Autozone. Anyone can read the computer codes, but only the experienced mechanics can diagnose the problem and figure out what is happening. Take it to the dealership and let them track this down. Both of those codes could be something like a spark plug wire (lean) or internal transmission issue like a solenoid problem . Keep us posted as to what they find out.

  6. Stephanie says:

    I don’t know if it matters, but my car is still under 75K miles. (Lol…I kinda forgot to add that in when I was writing my first comment.)

  7. Stephanie says:

    I’m so glad I’m not the only one with this problem; I thought I was going crazy! I just bought a 2001 Sonata (as my first car) in April and now, not even four months of owning it, I’m getting that jerking motion. It only happens after I let the car sit overnight. I go in reverse down the driveway, get on the street, switch to drive, and try to go and it feels like the car just wants to give up. After I somehow get to 20mph it jerks a little and then it works itself out.

    My check engine light has been on for about a month, but I think my car is getting worse so I decided to tell my friend about it, see what he said, and Google it. I found a site that said that the automatic transmissions on 2001 Sonatas may have problems going into reverse or drive after being parked for a few hours because the torque converter drains down through the front pump. I have no idea what that means, but it sounded like my problem so I thought I’d keep it in mind. After reading all of these comments I’m afraid to even get the codes read because I don’t want to deal with the expense of paying for a new transmission while trying to go to college.

    • Austin says:

      I hear ya, but you really have to start with reading the computer codes. This COULD be a costly transmission problem like some of the others are experiencing or this could be something as simple as bad spark plug wires causing an engine miss which would cause a similar complaint. I would also highly recommend you get the computer codes read at a Hyundai dealership, I am not sure if there is a recall or anything BUT if there is the dealer will know about it before anyone else.

      If you do get codes for internal transmission problems, you might talk to the dealership about changing the transmission fluid and adding a transmission fluid additive that Hyundai sells. There is a possibility that the previous owner had the transmission fluid changed, but used the wrong fluid type. This recently happened to my neighbor and a Subaru he purchased, the fluid looked good and clean but it was the wrong type of fluid for the vehicle and caused a strange haphazard shifting problem until he changed the fluid. Just a thought.

  8. joe says:

    i just put a motor in a 2002 hyundai sonata now it takes a while to shift into gear took it for a drive and it totally stopped moving trans fluid is full and check engine light is on and i was told sense the battery was un hooked for so long that the tcm might need to be flashed so it works right again

    • Austin says:

      Sorry for my delay, was out of town. I am not a transmission guy, but would suspect an installation problem with the torque converter possibly. I have heard that some GM vehicles will require a flash, but not sure about Hyundai. I would rule out everything else, installation or linkage problem, maybe a sensor unhooked etc. etc. If you can get the vehicle moving again, I would take a normal drive around the block, stop and and reverse, then take on freeway and see what happens.

  9. Denise says:

    I have the same problem. My husband sometimes thinks I’m crazy. Now I understand the safe mode 3rd gear. He says there is nothing wrong leaving the light on and running the car like this, but if I pull over and restart my 2000 Hyundai Sonata, the chechk engine light goes out until it jerks again and comes right back on. That’s is when acceleration is slow and feels like it’s dragging or lagging behind until you get going faster. This has been going on like this for over a year now and idling is rough. Yes, the car is a little better once warmed up. My car also hates the rain. I have to spray WD40 on all my wires before and after the rain. I had a new some kind of copper wire core put in and I still have problems. GRRRR!!!
    Wish I could fix it. I like the car but am thinking bout trading it in.

    • Austin says:

      This might not be a transmission issue, but rather a need for a tune up. If water is getting on the spark plug wires and causing a missfire, then the wires need to be changed out…and probably the spark plugs and distributor cap and rotor if you have them. I would also clean the throttle body to help smooth out the idle speed. Wait, you said you replaced the wires….just re-read that. You DO NOT want to spray WD 40 on the wires, its flammable and will start a fire!!! You can try spraying silicone spray on them to keep out any moisture, but there really should not be much moisture under the hood unless a plastic splash shield under the vehicle is missing or damaged. A new fuel filter might also be called for at this time interval.

  10. Jackie says:

    I have a 2001 Sonata and it dose the SAME thing I am on the fence on buying a new car becaue of this problem it is scary when your drivng down the highway and it happens I just dont feel safe with my 2 year old in it anymore time to upgrade I think. I HATE this car I have had it for 6 years and NOTHING but problems with it…This sencer and that sencer one thing after another it seems I am sick of it really! and you can 3x’S the parts to fix it too gotta love imports 😐

  11. andrea says:

    I have a 2001 sonata…I just got this car used in august its now october and iin that period…things have been going on with the car that I cannot explain…first of all the transmission…I’m glad I found this website because my mom and step dad drove it and so did my mechanic ande they were telling me that I was over reacting…I thought I was going crazy…the tranny when I first put my foot to the pedal the car jerks forcefully…then the car sounds like it is in the wrong gear and revs real hard and in order dor it to finally shift I kindaq have to tap the pedal and give a lil nudge and then the car shifts fine…also I recently went on a road trip and while in cruise control the car would down shift and u could hear the motor bogg down…then just a lil bit afterwards the car is now doin some. Steven king’s “christine” type stuff where out of no where when you tturn tyhe car on the car the dash lights flick on and off and the door sensor goes off and theere is a clicking noise…this only used to do this when the key was in the ignition…but now it’s doin it outta nowhere and its runnin down my battery…is ny car possessed or can somebody help me?

    • Austin says:

      I am affraid the only thing I can suggest is take it to the dealer and get a computer diagnosis. Hopefully this is something simple. Sorry I could not be more help. 🙁

  12. Fred says:

    I have a 2001 Sonata with the same jerky motion which can occur at any time. Finally check engine light has come on and the code p0705 (Transmission range sensor)and p0171B have appeared.

  13. tg1003 says:

    I purchased the 2000 Sonata gls 2 weeks ago, and have had nothing but problems. I had an emission related problem code, fixed that for 200.00. When I was leaving the service garage the car jerked into 1st gear and check engine light came on. Took it back, he scanned it, code no. P0720, mechanic drove, car was fine. Brought it back to mechanic yesterday to fix. He says he cannot fix the problem. Claims he scanned again, numerous codes are now coming up. He thinks it’s some sort of computer malfunction. Car jerked again while driving on the way home today. Now I am taking this piece of crap to the dealership.

    • Austin says:

      Don’t jump to conclusions to quickly, this could be something as simple as a bad spark plug wire causing an engine miss which can feel like a transmission problem. its not unusual at all to get multiple computer codes at once, you just have to clear the memory and see which ones continue to return…..and why. Pretty normal actually so don’t take it personally, hopefully its a simple fix.

  14. mike says:

    i have the same problem you might want to look in to transmission control module that is what my transmission shop said

  15. brock says:

    I have a 01 Hyundai elantra. It is popping the p0720 code after the tranny shifts itself into second. The tranny then oges into safe mode of 3 rd gear. It is fairly well documented online that this is most likely either output/or input speed sensor. Hyundai even has a service bulletin on it. It tells you to test the ohms on the wiring harness between tcm(transmission control module) and sensors. Less than 1 ohm replace harness, If you have proper resistance replace the sensors. I replaced my sensors and did not fix the problem. Hyundai fails to sales a replacement harness for the sensors. You must buy the whole wiring harness for the car at 1300. I am out of ideas, and don’t want to invest to much money into a car thats not worth it. Anybody familiar have any ideas?

    • Austin says:

      Sorry but I don’t have any personal experience with this issue. Hopefully someone else can post and help out here. If you do fix it please come back and post the solution. Thanks

  16. Joel says:

    2001 Sonata 4 cyl Canada Model. Shifts hard, usually only on the first acceleration after a cold start. Mechanics have no idea, took it to Hyundai, they flushed the tranny. Took away the problem for a week or less.

    Car now chugs when started and almost won’t accelerate. We replaced the fuel filter and the air filter. We also cleaned the mass air low sensor. The car runs well once warm but condition repeats itself wen cold. Any ideas?

  17. John says:

    I have had the same problem with our car (2001 Sonata 4cyl) and have been told repeatedly (at least 10 times) that “we can’t find any problem”. I have brought my car to the dealer since 40k miles with this problem. NOW that my warranty is gone they all of a sudden find that my trans is shot and refuse to fix it. I have a lawsuit pending with my local dealer. Oh..and my car only has 70k miles on it at this point. This is a known problem…they just stall you until your warranty is gone.

  18. Victoria says:

    This is interesting, I have an 02 Sonata that shifts like this. We call it a “bunny hop” and we sit in anticipation of it when we’re driving…it can really jolt you at times.
    My check engine light is now on and despite being re-set it came right back on, I just paid for my tags but can’t pick them up until I pass the smog test but I can’t have my car smog tested with the light on, it’s illegal here! We had it DX’d and they said it was the speed input/output sensor so we had it replaced, light is still on. The mechanic told us it’s our transmission and that it needs replacing. We’re going back and forth with what to do, this car’s been nothing but a money pit for us and it’s got under 80K on it so it hasn’t been heavily driven over the years.

    • admin says:

      I would suggest you see the dealership and let them diagnose the problem for you, you can always have another cheaper mechanic perform the repair once you know exactly what the problem is. This could be something as simple as a bad spark plug wire causing an engine missfire.

  19. Daniel says:

    I have a 2000 Sonata GLS V6 as well, and mine does something very similar, it will abruptly shift when cruising, from 4th to 3rd or vise versa, i mean ABRUPTLY. When it does this the check engine light comes on and it throws 3 codes u3900, p0705 and p0715, the first code is unknown, the second transmission range sensor and the third is the speed sensor, peculiar huh….

    • admin says:

      I am not a “transmission mechanic” but I would suspect an internal transmission issue causing this problem. This could be an expensive transmission to overhaul so I highly suggest you get 3 quotes AND 3 separate diagnosis before you jump in and overhaul this transmission.

  20. De'Shawn says:

    Sounds like the transmission is slipping or the fluid could be low.

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