Just wanted to return a repair post to the forum.

Problem: a "clunking" transmission while driving, and the Check Engine light coming on. Car no longer shifts and from a stop light its in 3rd gear (safety/default gear)

for months, I could reset the error by pulling off the road, find a parking lot and turn off the car and then back on. This got old fast....

Sometimes the error would reoccur, but it seems it was about once or twice a day maximum.
The check engine light would go off after killing then restarting the car.
I'd be driving along 40 or 70mph and "clank!!!" the car would shift as if going to 2nd.??? it would then no longer go to passing gear or anything.
This turned out to be a "safe/default" I guess per reading.

Anyway, finally had enough and went to AutoZone.
the AutoZone FREE code read showed a 0715, Input Speed Sensor.
Several posters said spend the extra $15-$20 less and get a Hyundai part.

Hyundai sells it for $100, or $95ish...AutoZone was a little cheaper, $15 less, and OReillys has to order it.
Its a small black plastic piece that literally pops in and pops out of a hole in the transmission case! not much to the installation of it as many said . 40minutes approx. very easy. An o-ring, already on the new part, maintains the seat/seal. Only one 10mm bolt holds it down.

INSTALL notes:
1qty 1/2ish socket to remove the larger brackets, one 10mm socket (for the sensor and air filter removal)
40minute job for a non-professional with some skill with a tool.

Remove the air filter lid, remove the air filter, remove the 3 bolts in the lower air filter housing, then below (in the greasy part of the engine) remove the cable bracket 2bolts and push cables to the side. The INPUT SENSOR is there with the connector pointing up.
>unplug the sensor
>removed the 1qty 10mm bolt, remove the sensor by wiggling it out (rubber o-ring holding it in)
>reinstall the new sensor, snuggin down with the bolt
>plug in the connector
reinstall the 2qty 1/2bolts/bracket....reinstall the air filter housing, air filter, then air filter lid.

go drive your car.


My own findings added a small bit of surprise, and not documented, imo.

The two sensors, INPUT & OUTPUT, are not interchangeable.
The INPUT has the connector pointing upward, the OUPUT has its connector protruding from the side.

More important the 10mm bolt holes do not align the same.

To clarify for the novice, like myself, on the 2001 Elantra, the Output Speed sensor is closest to the firewall/master brake cylinder.

by mistakenly removing the output sensor first, I found the bolt mounting holes don't align between the output and input sensors.....they are not interchangeable. I also cracked the connector trying to force the plug onto the wrong sensor.

Even though they look close to the same, and some posters say they are interchangeable they are NOT.

I reinstalled the Output sensor, its only one 10mm bolt..and went on to do the job right

I cussed a bit....

then found the INPUT Sensor, about 14" towards the front/bumper side of the transmission. It was kind of hidden under a cable bracket which I removed, 2qty greasy bolts.

making sure not to have any crap fall into the hole, I wiggled the old INPUT sensor out. and quickly stuffed the new sensor in, to fill the hole quickly to prevent debris from going in..
snugged down the 10mm bolt and reconnected the plastic cable/plug.
40 min.

went for a joy ride and all seems to be fixed.

as I understand it, if these sensors skip 1 second, the car goes to a default gear (3rd I think) and won't shift anymore, sending code errors.
one error code so the dash to lite up Check Engine, other codes to say it was the INPUT or maybe the OUTPUT etc...

anyway, hope this helps the next person. I was very grateful for all the info people had posted. It helped me save about $300 and hours at the Hyundai shop (I got a quote before doing it myself).



time to repair 40minutes like most posters said.
my cost for an OEM part was $95 from Hyundai. INPUT SPEED SENSOR
pretty cool, imo.

 

well spoke/wrote too soon!

After quite a bit of driving, the error happened again.

Now the code says its the Output Speed Sensor...

I noticed something new though, it seemed the speedometer stuck at 60mph for a second or two,, kind of odd. Maybe related ?

I'm going to unplug the negative battery lead and allow it to fully reset.

Drive again tomorrow and then if the error occurs again, replace the Output Speed Sensor....arrrg

 

cont...

after a pretty good slam this morning, and a couple more check engine lights...back to AutoZone for a free code check.

again now it sates the Output Speed Sensor. So I bought one installed it in about 10 mins. $90.

not so quick to say its fixed this time.

 

ok. I think I can say its fixed this time. Over 100 miles and numerous days of various speeds and traffic.

So $190 for the Input and Output speed sensors.

I was also reading a friends Edmunds repair guide on these Transmission speed sensors, and it showed a way to actually test the sensor, I never did this but it is worth noting.

 

Thanks for the advice pal. I thought that the ABS speed sensor and the output was interchangeable. Maybe that's why I was not able to fix it.

 

Thanks to all for the great advice about changing the Input and Output sensors. I had a mechanic change my Output sensor about nine months a go. Three weeks ago it failed again. So I searched and came across this forum. I saved myself over $200 in labor charges by changing both sensors myself - with the help of all you folks experiencing the same problem. I drove the car for about 20 miles and no problems yet.

But I'm still worried that it will happen again, so I'm contemplating either trading or selling the car, although it's been a good runner.

Has the problem gone away for long periods of time (over one year, at least) for most of you folks? Or is it a continual problem?

 

Mine hasnt returned .....

I do wonder if the sensor on the wheel will go though. There is one more sensor to this "system" I think.

I'm a 50/50 mechanic...50% right....

I appreciate these forums too.

Right now I need strut help!! the back end "froze up" after a mechanic shop had the car in the air using a X type life...where the wheels are NOT supported...

arrrrrggggg

 

Elantraman!

I'm having this problem and I'd like to fix it myself. Quick question though, are the output and input speed sensor in the same place?

I'm getting troublecodes P0720....which is the output. From what I could tell, you made it sound like they were in the same area?

Thanks for the information.