[DakotaDillard]

I recently bought an 03 Hyundai Tiburon 2.7 GT with the automatic, 126,000 miles. Car is throwing a code p0720. The owner before me replaced both input and output sensors twice. I cannot figure out what’s causing the limp mode. Drained fluid replaced it. Checked wiring and harnesses. At first it would drive fine for about 8-10 miles then randomly pop into 3rd(limp mode). Turn it off restart it, drives fine shifts fine then back to 3rd. Recently it has been not wanting to shift at all and when i can get it to using sport mode it will drop to first while I’m driving. No check engine light when that happens. I don’t have any money to sink into this think. Anyone who has dealt with this and figured it out please contact me. Was considering a wheel speed sensor because the previous owner hopped a few curbs. But it’s not throwing an abs sensor code and the light isn’t on.

 

[The_Evenger]

Does your speedometer drop out when the code trips?
Does the transmission go into limp mode quicker or stay in limp mode after the 8-10 miles of driving?
Were the sensors replaced with OEM parts?

Right off the bat I'd be suspecting a faulty output shaft sensor or damaged wiring. I'm not sure how sensitive the TCM is to sensor brands, but I know the ECM is really picky with sensors. So if the output shaft sensor was replaced with a bargain brand, well that might be your issue. They don't usually go bad though, so I'm wondering if there's a wiring problem on the harness. it would be worth doing a visual inspection to see if you can see any places the harness has been rubbing on something.

 

[DakotaDillard]

Does your speedometer drop out when the code trips?
Does the transmission go into limp mode quicker or stay in limp mode after the 8-10 miles of driving?
Were the sensors replaced with OEM parts?

Right off the bat I'd be suspecting a faulty output shaft sensor or damaged wiring. I'm not sure how sensitive the TCM is to sensor brands, but I know the ECM is really picky with sensors. So if the output shaft sensor was replaced with a bargain brand, well that might be your issue. They don't usually go bad though, so I'm wondering if there's a wiring problem on the harness. it would be worth doing a visual inspection to see if you can see any places the harness has been rubbing on something.

 

[DakotaDillard]

Output sensor and input were replaced with oem twice. Me and my buddy also checked out the wiring as best as we could. Checked fuse box, all the grounds we could find. What I don’t understand is out of can drive perfectly fine, like shift through every gear fine and then randomly throw the code. Does the abs wheel speed sensor affect the output shaft sensor? I saw one thread where someone had to replace a wss to fix his problem. I just don’t have a lot of experience as a mechanic myself and I can’t afford to take pay someone to diagnose it.

 

[DakotaDillard]

Output sensor and input were replaced with oem twice. Me and my buddy also checked out the wiring as best as we could. Checked fuse box, all the grounds we could find. What I don’t understand is out of can drive perfectly fine, like shift through every gear fine and then randomly throw the code. Does the abs wheel speed sensor affect the output shaft sensor? I saw one thread where someone had to replace a wss to fix his problem. I just don’t have a lot of experience as a mechanic myself and I can’t afford to take pay someone to diagnose it.

And speedometer doesn’t jerk around or anything.

 

[The_Evenger]

I don't know about the WSS affecting the TCM. I guess it could be possible but I wouldn't think the TCM would care about any WSS, I believe the ECU does use the right front WSS. All I can think of is either a wiring harness that's rubbed through or a flaky ground that's slowly warming up during your drive.