Jun 8, 2008

sonata vehicle speed sensor

I was driving Kiri's car (an '02 Sonata) not too long ago and, suddenly, the speedometer dropped to zero. A few seconds later the check engine light came on. The car also started idling at very low rpm, but I'm not sure if that was related. I had taken the car to the dealer with the airbag issue and immediately suspected them of accidentally screwing it up or giving themselves a little job security. Either way, I didn't want to take it back. I began searching online and found that there are actually three speed sensors on a Hyundai Sonata.

Conveniently, Sonatas do not have repair manuals. Instead, Hyundai provides a cryptic website for diagnostic and repair info. Anyways, the input and output sensors are located on the transmission and help your vehicle know when to shift. Much information regarding these two sensors can be found in online forums and even on the crappy Hyundai service website. Little to no information, however, can be found for the third sensor: the vehicle speed sensor. Fortunately for me, I had a vehicle speed sensor problem. I'm writing this post to maybe save somebody the headache of trying to figure it out on their own. Most of the information I received from conversations with dealer service department people and one particularly helpful dealer mechanic who walked out to my car with me and showed me where the sensor was and described how to fix it. I have a 2002 Sonata and I imagine this applies to all automatic Sonatas with the same body style.

The vehicle speed sensor is located on top of the transmission as shown in the picture below:

Click on the image for a larger view. The sensor is circled in yellow. I began by disconnecting the air filter hose and removing the top of the air filter housing. This gave me better access to the sensor. A close view of the sensor can be seen below:

To remove the speed sensor, I disconnected the electrical plug from the sensor using a flat head screw driver, taking care to not damage the plug. The plug came off easily. If the terminals on the plug look corroded, it's a good idea to clean them and reseat the plug, as a bad connection may have been the only problem. If that doesn't work, keep reading.

Because the sensor plugs into the top of the transmission, it is a good idea to clean the area around the sensor to prevent dirt from entering the transmission when the sensor is removed. Next, I removed the bolt which holds the sensor in place.

The speed sensor assembly is comprised of the speed sensor and a plastic gear. The plastic gear is turned by the transmission. The sensor measures the speed of the shaft on the plastic gear which is held in place by a retaining ring. I purchased both the sensor and the gear for good measure. The new speed sensor assembly is shown below:

The white helical gear can be seen on the right and, just to the left of it, the retaining ring which holds the small gear shaft on the sensor.

After removing the bolt from the transmission, I removed the sensor assembly by gently prying it upward with a flat head screw driver. When I removed the retaining ring and gear from the sensor, small pieces of broken plastic fell out of the sensor. I guess that was my problem (it's good to know the dealer probably wasn't pulling a fast one). The disassembled speed sensor assembly removed from the car is shown below:

The old speed sensor was covered in transmission fluid. So, for good measure, I applied fresh transmission fluid to the o-ring on the new sensor, gear shaft and helical gear. I then inserted the shaft in the speed sensor, installed the keeper ring and installed the assembly by reversing the removal procedure. When the car was put back together, I started the engine, the check engine light turned off and the speedometer worked perfectly!

For those unfortunate enough to own a Sonata, I hope this tutorial helps.

32 comments:

erock said...

I'm impressed. Looks like that Mechanical Engineering degree is really paying off. :-)

Ogre said...

Now what are the odds i wll ever need this information

David & Jana said...

I'm so impressed! Seriously.
"Chicks dig guys with skills!"
I bet it's nice for Kiri to know she has such an awesome husband.:)

Lgrins said...

Your right, there is not enough information made available to repair such an issue. I have a 97 Sonata and I've been driving around without a speedometer for some time now. I use the tach and also gauge my speed by others on the road. I did not know where the sensor was so I haven't fixed it. My speedometer rarely works. I'll look at it in the morning and see if I have something similar. Thanks for your post. LG

pilgrimnprogress said...

My 2003 Sonata speedometer started intermittently bouncing around,zeroing out & disengaging my cruise control. The dealer wanted $100 just to hook it up to his diagnostic scanner and warned he could not attempt repair unless he could prove that the vehicle speed sensor was defective. With the help of your grreat instructions, I replaced it anyway for $100 and it has been perfect ever since. Thanks a millino fro the great job you've done.

vjm530 said...

Good stuff. Do you have the part numbers or any identity info on both the sensor and gear? Thanks.

BTW, I have a 2002 sonata GLS V6

aaron said...

Sorry. I don't. My car is a 4-cylinder. I doubt the tranny is the same. If you do have a speed sensor problem call the parts department at a dealer. They usually know what their talking about.

vjm530 said...

My problem is: While driving (at any speed) sometimes the speedo drops to 0 for a while (sometimes a minute or 2, sometimes longer) and then returns to normal. When this happens the rpm's are still registering but not the mileage or speed. No warning lights, no engine/transmission change or any other indication that something is wrong other than what I explained above. Is this something to worry about or . . . ?

pilgrimnprogress said...

I bought the new part Aaron described from the dealer($125.00) & paid my mechanic $75 to install it. I could have done it myself using posted instructions but was facing a speeding ticket & this was my defense. According to my mechanic, the insides "core out" permitting the sensor to disengage. It will continue to get worse & your cruise control won't work properly.

RITA said...

There are 2 speed sonsors, one the input and one the output. What you replaced was the output speed sensor.

aaron said...

Actually, there is an input speed sensor, output speed sensor and a vehicle speed sensor (3 total) on the transmission. What I replaced is the vehicle speed sensor.

aaron said...

Log in to hmaservice.com

Select the "Service Information" tab

Enter your vehicle in the vehicle bar - Choose Sonata(EF), 2002, G 2.4 DOHC

Select "DTC" from menu bar just above the vehicle selection bar.

Select "Transmission > Automatic Transaxle" from the listed options

Select "P0715 A/T Input Speed Sensor Circuit Malfunction" or "P0720 A/T Output Speed Sensor Circuit Malfunction"

Select "General Information" to see a photograph of the input/output speed sensor locations.

"General Information" also contains valuable information on the purpose of the sensors and how they interact with the vehicle speed sensor.

The vehicle speed sensor is not either of those locations. A schematic diagram with the vehicle speed sensor can be found in the "ETM" section under "Vehicle Speed Sensor System".

Todd McLain said...

GENIUS, this is exactly what I need. Thanks for your contribution to mankind and beyond. Will keep you updated with how it goes...

Jay Groove said...

Absolutely awesome. You and I are kindred spirits. When I successfully make it through a challenge like this (particularly since I'm not well-versed with auto mechanics), I hope the info will save at least one person from just downing a six-pack and giving up.

Thanks!

The Referee said...

my son's car is giving me a P0502 error. I believe it is this sensor, but I didn't know the location. You may have just saved me a ton of time and money.

amateursarto said...

What if its giving you no error code? Its just clunking thru first gear and then it shifts fine. This only happens at startup and then every once in a while intermittently. The trann fluid is ok, but there's that thunk....

Asiwaju said...

Aaron,i live in Africa and i drive a sonata 2003 model. the problem with my car is that 1.) when you shift the gear onto drive it takes approximately 3 seconds for it to engage with a jerk movement.2.)when it moves for about 5minutes, it stops moving. but the reverse gear moves. 3.)Also it doesn't shift from 1-2 in the drive mode. when you manually shift it to gear 2 and move the gear lever back to D, it will select from 2-3 and 4 and back to 3-2 when it gets to 1 again, same occurrence happens.
Is it the sensor? or the transmission has packed up?

Randy said...

Thanks Aaron. Well written and very informative. Eager to replace this part and see the results. Keep up the good work.

hany said...

thank u so much thi sis so helpful but i just observed thi sis a common faliure in sonata and this i sbad reputition for sonata i hope my next car will not be hyundai

hany said...

Thank u so much i ll try to do it soon but i observed this is a common faliure in sonata so its a very bad reputionm to huyndai i hope my next car will not be hyundai

CacaMonster said...

Hey man Greattt work.

but could you tell me where the other 2 sensors are located?

and what is the purpose of all 3
if you have time.

I own a 2001 hyundai sonata and am having some tranny problems. :/

Karthik said...

Saved me a lot of money. I had the same issue as you did. Ironically I had an airbag issue too. I wonder if these are related to the 2002 Sonata's

Barb Foulds said...

This is the exact problem I have with my 1997 Sonata... once the car gets going, the speedometer drops to zero, or sometimes bounces around like crazy. I found a part online but I'm kind of terrified to try to fix it on my own... lol. Thanks for your post though. :)

bill dean said...

I also would like to know where the other 2 sensors are. I have a fully working speedometer but my check engine comes on and I have replaced the one you show on top of transmission and it still has the error code. The great state of Missouri flunks all cars on EMISSIONS if check engine light is on
Mine is a 6 cyl 2002 sonata d the 6cyl alsohave 3 sensrs?

Francis Capone said...

Aaron I have a 99 Hyundai Sonata do you know any way I could get a picture of where the input sensor goes on that year of Sonata I could really use the help thank you

William said...

Aaron I have a 2002 Sonata and I need the engine and tranmission replaced. Could you do the job if I get a you a six pack of Wal-mart's Dr. Thunder?

michael barnes said...

RE: bill dean,

Normally after completing a repair that has triggered a code, the procedure involves clearing the code using a code scanner. Many auto parts stores in the states will allow you to use their scanner for free. Once cleared, if the code reappears then obviously the procedure didn't solve the problem.

Technically, there are two types of codes... existing codes which trigger the light and pending codes which a scanner would read indicating there is not failure but a few out of parameter readings have been noted. Both codes will clear themselves after two or three driving cycles with no out of spec readings. A driving cycle is defined " something like : getting the vehicle up to 40/45 mph for 1/4 mile or so, slowing down to 10 mph then back to 45 etc. etc. The idea is to simulate a short city trip.

In my state the emissions facility can simply plug into your vehicle On Board Diagnostic port and look for codes. However, for vehicles pre-OBDII they still have to put the vehicle on a driving simulator. Perhaps you;ve seen them. They normally place a fan in front of the vehicle for temperature control, a hose over the exhaust and put the drive wheels on a set of rollers. Then they drive the vehicle in place while watching a monitor. It looks like they are playing a video game, accelerating and decelerating to keep the vehicle on the monitor between the lines. THAT series of speed-up/slow down maneuvers IS one driving cycle. It allows them to measure all phases of operation, accelerating, decelerating at different levels, each which produces a different emission result.

Ivantorre said...

Hi, i live in brasil and i need a speed gear with 29 teeth for 1999 sonata 2.5 v6. The sensor with gear looks like the one in the picture. Is it for sale?
Im open for suggestions.
Thank You very Much.
Ivan torre

Das said...

Great write up! This is really helpful, but how did you get the bottom air filter box (air cleaner body) removed to get to it? I see bolts on top right and bottom left. I assume there is one more somewhere that is holding down. Thanks again.

lastgem31 said...

Thank you, Aaron. Your blog was very helpful.

steve goodwin said...

Thanks Aaron you are the man! I was about to just junk it but I ran in to your blog thanks a million! There are still good people on earth lol

Jsk Automotive said...

That was an extremely interesting blog. Thanks for sharing...

Importer of Hyundai Car Parts