I recently had a CEL on my 2011 Kia Optima and also weird behavior with the A/T (gear indicator on dash was blank and sometimes the A/T wouldn’t automatically shift all the way down to 1 at stops sometimes). I bought my own code reader (only cost ~$30 on Amazon) and the code I got was P0705 which indicated a problem with the Transmission Range Sensor (TRS) which is also sometimes referred to as the Automatic Transmission Inhibitor Switch or the Neutral Safety Switch. This appears to be a pretty common problem on both Kia and Hyundai. Fortunately, the fix is really simple – all you have to do is swap out the TRS. On all these vehicles (Kia Optima, Kia Sorrento, Hyundai Elantra) the TRS is located in the front driver-side quadrant of the engine bay (the bottom-right if you are looking under the hood). To replace it, you simply need to remove the air intake, battery and battery holder and the TRS is right there just underneath the battery holder. If you know what you are doing and fast, this can be done in as little as 20 minutes although I really took my time and triple-checked everything.
The TRS is basically just a device which senses what position/gear the car is in and sends that information back to the computer. This allows the car to display the current gear on the dashboard and it may also prevent the car from starting if the computer believes that the car is not in Park/Neutral. I bought mine from kiapartsnow.com and it only cost ~$50 shipped. Aside from that part, the only tools you need are a ratcheting socket wrench (or driver) with 10mm, 12mm and 14mm sockets and also a small flat-head screwdriver (just to pop off the wire connecting the TRS).
For my vehicle, the current version of the part is 4270026700. The current version has metal housing and looks a lot more robust than the older version. The holes and connections all go in the same way. (Note that the OLD version of this is 4270026000 or -45956B. Do not use the older version as I believe those are more prone to have this problem again in the future.)
*** SAFETY WARNING ***
Absolutely make sure that you set the parking break AND chock the tires before starting. The reason why is that the TRS connects to the AT gear shift and it is easy to switch gears on accident while you are working on the vehicle and knock it out of park. In fact, that happened to me while I was working on mine.
*** STEPS ***
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1) Remove the air intake. Unscrew 2x 10mm bolts. Then lift the unit slightly up and pull it straight towards you. It will slide right out.
2) Disconnect the battery. Terminal connections are 2x 10mm. Remove negative first. Make sure you cover the terminals so that you don’t accidentally touch or short the battery.
3) Remove the battery. There is a retainer at the front of the base. 1x 12mm bolt.
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4) Remove the battery tray. 4x 12mm in the tray and 2x 10mm at the top. After removing the bolts, I just rested the battery tray out of the way towards the front.
![Image]()
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5) Remove the old TRS. 1x 14mm nut in the center. 2x 10mm bolts on the sides. Do NOT touch the nut on the right side of the arm – only the 1 nut and 2 bolts on the TRS itself. Once you remove those, lift off the arm and then lift off the TRS. Then disconnect the wire from the TRS – you will probably need a flat-head screwdriver to release the wire.
6) Install new TRS. If it doesn’t slide right back on, you might need to either wiggle it on or turn the hole in the center to line up with the bolt. Also, if the metal arm does not slide right back on the bolt, you may have bumped the center bolt (which controls the AT gear). Just use a vice grip or wrench to turn the gear back to the correct position. As long as the gear selection bolt is in the correct position, the arm should slide right back on. Once the TRS and arm are on, screw back in the 2 bolts and 1 nut. You might need to screw on the 2 bolts before attaching the arm.
7) Re-install battery tray. 6 bolts(4x 12m + 2x 10mm).
8) Re-install battery. 1 retaining clip and bolt. Then re-connect both wires – I attach positive first.
9) Re-install intake. Slide it back on and then 2 bolts.
10) When everything is done, take a test drive around the block to make sure everything is working. All gears should work and show up on the dashboard.
11) Reset the OBD “Permanent DTC”. If you don’t do this, the trouble code might stay in the computer (even if the CEL is gone) and you will NOT pass SMOG/Inspection. To do this you need to do the “Universal Trip Drive Pattern”: Start Car. Idle for 30+ seconds. Drive for 5+ minutes at normal speed (total drive time should be 10+ minutes). Idle car for 30+ seconds. Turn off. To verify that the “Permanent DTC” is removed, you will need to use a code reader.
*** RESOURCES and REFERENCES ***
OBD Code P0705:
https://www.obd-codes.com/p0705
This is the part that you need:
KIA TRS/AT Inhibitor 4270026700: https://www.kiapartsnow.com/genuine/kia-switch-inhibitor~4270026700.html
Optional if you want to replace these:
NUT: 1311FA https://www.kiapartsnow.com/genuine/kia-nut~1311110007k.html
WASHER: 1360CF https://www.kiapartsnow.com/genuine/kia-washer-spring~1360210006k.html
2 BOLTS: 1140EP https://www.kiapartsnow.com/genuine/kia-bolt~1140306226k.html
TSB: https://f01.justanswer.com/mbrauto/0db6607f-35cd-4cda-ad06-8296853b1864_2015_Kia_Sorento.pdf
Video showing replacement on Hyundai Elantra:
Pictures showing replacement on Kia Sorrento: https://www.kia-forums.com/2011-2013-xm-sorento-forum/208177-2011-kia-sorento-p0705.html
Another related thread: https://www.optimaforums.com/forum/170-service-center/166979-trs-warranty.html
How to remove Permanent DTC from computer: https://www.autoserviceworld.com/carsmagazine/taking-a-first-look-at-permanent-dtcs/
The TRS is basically just a device which senses what position/gear the car is in and sends that information back to the computer. This allows the car to display the current gear on the dashboard and it may also prevent the car from starting if the computer believes that the car is not in Park/Neutral. I bought mine from kiapartsnow.com and it only cost ~$50 shipped. Aside from that part, the only tools you need are a ratcheting socket wrench (or driver) with 10mm, 12mm and 14mm sockets and also a small flat-head screwdriver (just to pop off the wire connecting the TRS).
For my vehicle, the current version of the part is 4270026700. The current version has metal housing and looks a lot more robust than the older version. The holes and connections all go in the same way. (Note that the OLD version of this is 4270026000 or -45956B. Do not use the older version as I believe those are more prone to have this problem again in the future.)
*** SAFETY WARNING ***
Absolutely make sure that you set the parking break AND chock the tires before starting. The reason why is that the TRS connects to the AT gear shift and it is easy to switch gears on accident while you are working on the vehicle and knock it out of park. In fact, that happened to me while I was working on mine.
*** STEPS ***
1) Remove the air intake. Unscrew 2x 10mm bolts. Then lift the unit slightly up and pull it straight towards you. It will slide right out.
2) Disconnect the battery. Terminal connections are 2x 10mm. Remove negative first. Make sure you cover the terminals so that you don’t accidentally touch or short the battery.
3) Remove the battery. There is a retainer at the front of the base. 1x 12mm bolt.
4) Remove the battery tray. 4x 12mm in the tray and 2x 10mm at the top. After removing the bolts, I just rested the battery tray out of the way towards the front.
5) Remove the old TRS. 1x 14mm nut in the center. 2x 10mm bolts on the sides. Do NOT touch the nut on the right side of the arm – only the 1 nut and 2 bolts on the TRS itself. Once you remove those, lift off the arm and then lift off the TRS. Then disconnect the wire from the TRS – you will probably need a flat-head screwdriver to release the wire.
6) Install new TRS. If it doesn’t slide right back on, you might need to either wiggle it on or turn the hole in the center to line up with the bolt. Also, if the metal arm does not slide right back on the bolt, you may have bumped the center bolt (which controls the AT gear). Just use a vice grip or wrench to turn the gear back to the correct position. As long as the gear selection bolt is in the correct position, the arm should slide right back on. Once the TRS and arm are on, screw back in the 2 bolts and 1 nut. You might need to screw on the 2 bolts before attaching the arm.
7) Re-install battery tray. 6 bolts(4x 12m + 2x 10mm).
8) Re-install battery. 1 retaining clip and bolt. Then re-connect both wires – I attach positive first.
9) Re-install intake. Slide it back on and then 2 bolts.
10) When everything is done, take a test drive around the block to make sure everything is working. All gears should work and show up on the dashboard.
11) Reset the OBD “Permanent DTC”. If you don’t do this, the trouble code might stay in the computer (even if the CEL is gone) and you will NOT pass SMOG/Inspection. To do this you need to do the “Universal Trip Drive Pattern”: Start Car. Idle for 30+ seconds. Drive for 5+ minutes at normal speed (total drive time should be 10+ minutes). Idle car for 30+ seconds. Turn off. To verify that the “Permanent DTC” is removed, you will need to use a code reader.
*** RESOURCES and REFERENCES ***
OBD Code P0705:
https://www.obd-codes.com/p0705
This is the part that you need:
KIA TRS/AT Inhibitor 4270026700: https://www.kiapartsnow.com/genuine/kia-switch-inhibitor~4270026700.html
Optional if you want to replace these:
NUT: 1311FA https://www.kiapartsnow.com/genuine/kia-nut~1311110007k.html
WASHER: 1360CF https://www.kiapartsnow.com/genuine/kia-washer-spring~1360210006k.html
2 BOLTS: 1140EP https://www.kiapartsnow.com/genuine/kia-bolt~1140306226k.html
TSB: https://f01.justanswer.com/mbrauto/0db6607f-35cd-4cda-ad06-8296853b1864_2015_Kia_Sorento.pdf
Video showing replacement on Hyundai Elantra:
Pictures showing replacement on Kia Sorrento: https://www.kia-forums.com/2011-2013-xm-sorento-forum/208177-2011-kia-sorento-p0705.html
Another related thread: https://www.optimaforums.com/forum/170-service-center/166979-trs-warranty.html
How to remove Permanent DTC from computer: https://www.autoserviceworld.com/carsmagazine/taking-a-first-look-at-permanent-dtcs/
