Have a 01 Tiburon..when overdrive button is on goes into neutral when I turn it off shifts fine except wont go into overdrive..

OD clutches are gone, leaks at the valve body, Or bad seal for OD.

run the fault codes as there may be a problem i he VSS or TCM module

Hi, Try changing the oil in the transmission and filter. Good luck.

It is the shift solenoid.. the solenoids are like a fuse and they pop easy and go bad all the time

it sounds like transmission trouble take it to a shop cause i dont think you wil have the tools to fix the trans at home

Check the help link mentioned below:----

Overdrive light in the dash blinks?

http://repairhelpcenter.blogspot.com/2012/01/overdrive-light-in-dash-blinks.html

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OD light flashing and transmission fluid leaking?

http://repairhelpcenter.blogspot.in/2012/02/od-light-flashing-and-transmission.html

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Also i suggest you to refer these gear shift issues, which are mostly noticed. These are direct links with appropriate solutions to the specific problems of gear ****.

GEAR SHIFT ISSUES

Gear indicator Shows "3" Instead Of "D"?

http://whoisbyme.blogspot.in/2012/07/gear-indicator-shows-3-instead-of-d.html

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2006 Chrysler 300c: Shifter Stuck in Park?

http://technoanswers.blogspot.in/2012/06/2006-chrysler-300c-shifter-stuck-in.html

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1998 Ford Expedition: Will not Shift Out of Park?

http://schematicsdiagram.blogspot.in/2012/06/1998-ford-expedition-will-not-shift-out.html

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Car will not move when in gear?

http://repairhelpcenter.blogspot.in/2012/02/car-will-not-move-when-in-gear.html

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Mercedes-Benz transmission sticks in first gear?

http://technoanswers.blogspot.com/2012/01/mercedes-benz-transmission-sticks-in.html

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Mercedes Benz not engaging in first gear?

http://technoanswers.blogspot.com/2012/01/mercedes-benz-not-engaging-in-first.html

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Chrysler PT Cruiser only goes in First gear?

http://howtobyme.blogspot.com/2011/11/chrysler-pt-cruiser-only-goes-in-first.html

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Car is stuck in park and the shift will not move?

http://howtobyme.blogspot.com/2011/08/car-is-stuck-in-park-and-shift-will-not.html

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2007 Ford Expedition: How to shift car in neutral with Dead Battery

http://www.howtorepairguide.com/2012/11/2007-ford-expedition-how-to-shift-car.html

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2002 Nissan sentra will not go out of park mode?

http://technoanswers.blogspot.in/2012/02/2002-nissan-sentra-will-not-go-out-of.html

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Nissan Sentra stuck in park?

http://technoanswers.blogspot.in/2012/02/nissan-sentra-stuck-in-park.html

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Car will not come out of Park?

http://howtobyme.blogspot.com/2011/11/car-will-not-come-out-of-park.html

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Automatic transmission will not go into high gear?

http://howtobyme.blogspot.com/2011/11/automatic-transmission-will-not-go-into.html

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Car won't downshift sometimes?

http://schematicsdiagram.blogspot.com/2011/12/car-wont-downshift-sometimes.html

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Buick Park Avenue: Transmission will Not shift into drive?

http://schematicsdiagram.blogspot.com/2011/12/buick-park-avenuetransmission-will.html

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No First gear Starts In Second Gear

http://www.howtobyme.blogspot.com/2012/07/no-first-gear-starts-in-second-gear.html

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Ford Taurus won't shift from park?

http://schematicsdiagram.blogspot.com/2011/12/ford-taurus-wont-shift-from-park.html

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2006 Ford F150: Will Not Shift out Of Park?

http://technoanswers.blogspot.in/2012/06/2006-ford-f150-will-not-shift-out-of.html

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Car Transmission will not go into Park mode?

http://schematicsdiagram.blogspot.com/2011/12/car-transmission-will-no-go-into-park.html

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1998 Chrysler Voyager: Transmission Problem?

http://howtobyme.blogspot.in/2012/06/1998-chrysler-voyager-transmission.html

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Shift indicator directly goes to 2nd when key is turned ON?

http://schematicsdiagram.blogspot.com/2011/12/shift-indicator-directly-goes-to-2nd.html

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Third gear missing and engine losing power?

http://schematicsdiagram.blogspot.com/2012/01/third-gear-missing-and-engine-losing.html

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Chevrolet silverado has whining sound in gear?

http://technoanswers.blogspot.com/2012/01/chevrolet-silverado-has-whining-sound.html

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2002 Chevrolet Avalanche Z71: Gear shift Issue?

http://whoisbyme.blogspot.in/2012/06/2002-chevrolet-avalanche-z71-gear-shift.html

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Hard to shift gears on Manual transmission?

http://technoanswers.blogspot.com/2012/01/hard-to-shift-gears-on-manual.html

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Car hard shift at slow speeds?

http://technoanswers.blogspot.com/2012/01/car-hard-shift-at-slow-speeds.html

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Transmission-Hard To Down Shift

http://technoanswers.blogspot.in/2012/07/transmission-hard-to-down-shift.html

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Automatic transmission shift lever hard to move on cold mornings?

http://technoanswers.blogspot.com/2012/01/automatic-transmission-shift-lever-hard.html

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2000 Nissan maxima shifts hard?

http://schematicsdiagram.blogspot.in/2012/02/2000-nissan-maxima-shifts-hard.html

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Vehicle noticed sluggish delayed shifts while driving?

http://schematicsdiagram.blogspot.in/2012/03/vehicle-noticed-sluggish-delayed-shifts.html

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2007 Hyundai Santa Fe: Will not Shift out of Park Mode?

http://schematicsdiagram.blogspot.in/2012/06/2007-hyundai-santa-fe-will-not-shift.html

These details will help.

Thanks.

I would check into the Trans oil temp sensor,they are known to keep the trans from shifting into 4th gear if they have a open or a shorted circuit...This may also be the culprit for the other issues you are experiencing when the trans is at diff temps and doing diff things....The other thing that is known for going bad in that Transaxle is the Sunshell...The splines on the inside of the sunshell strip out and than you will lose pretty much all forward gears,Except for 1st gear most likely and you will also lose Reverse if the Sunshell goes bad...But this will not act any different if the temperature is cold or hot

I think rebuild try and service it if you find any lining material in the pan bad news

this is a hard mechanical fault in the overdrive forward clutch, u must overhaul the trans to fix this.

Okay, I baught an 01' tiburon last march. When I first had trouble with the tranny it wouldnt shift into fourth and no it wasnt the overdrive button. Then it started downshiftling like what your experiencing then I lost reverse. Ammco rebuilt the tranny. I would take it to them, they will inspect it for free. You may just need a tran fluid flush. You should know that in the automatics the tranny is the weakest part of the car. The engines are great, just everything around them seems to fall apart after 120,000 miles.
Ammco offers a free inspection service. However Just from experience - if you need a new auto tranny it is cheaper to buy one already rebuilt (with warrantee) and pay to have it installed than to rebuild the one you have.
Cheers to hyundai challenge : )