P0734 4th gear problem, transmission needs replacement?
 

Hi all, I got an old 2001 hyundai accent 1.6L with automatic transmission and over 170k. This car drives fine until recently. When I drive on the highway last week the engine suddenly revs up to 45k even though my speed is only about 65~70MPH. The check engine light comes on. I drove home that day despite of all these and took the car to autozone for a code check very next morning. They said there's an engine misfire and TCM error code P0734 which means the 4th gear is not engaging right. The engine misfire is likely caused by the TCM error code so it all boils down to the transmission. By the way, I do notice there's a clicking sound when I release my foot from the gas pedal(when the car's moving) and the clicking sound does seem to correlate to the actual wheel rotation speed(ie, when the car's faster, the clicks are more rapid). When I put my foot back on the gas, the sound goes away.

Then I did some research on the internet. It seems this is a very common transmission failure for hyundai cars. Some are caused by bad soleinoids but most are caused by an internal failure of the transmission, which means the whole transmission needs to be replaced. Given this car is very old(but drives fine until recently), I probably need to dispose it if it needs a transmission replacement. Even used transmissions cost over $1k plus labor(which is about another $500), and I don't know how much longer the car can drive if the transmission is replaced. I've read from somewhere that someone has managed to replace a bearing inside the transmission and said it wasn't too difficult to do so. I can't seem to find that thread anymore so I would like to ask:

1. how difficult is it to check the transmission's gears. I understand I must jack up the car, put it on jack stands, remove the driver side tire and remove some boits on the transmission assembly. I just want to know do i need any special tools other than common torque wrench and sockets?

2. how to check for the blown bearing and pin? can someone post some photos what inside of the transmission are supposed to look like?

3. How to rule out the solenoids malfunction? I prefer to repair the solenoids if that's where the problems are. Never opened up a tranny before so I'm not sure how difficult it is. I don't think its 'the speed sensor/pulse generator because there's no readings of error codes for them.

I would appreciate any input. I had this car for a long time and invested a lot of money in it. This car is like my old friend. So letting it go now is a rather sad feeling. if I can fix it(I'm not an auto mechanic but has done many repair jobs myself), that will be a very proud achievement.

2001 Tiburon, same code
 

I got the same code on my 2001 Tiburon. It's been shifting from 2nd down to 1st really rough.There has not been a service engine light on at all, but i still wanted to have it scanned for any codes. But the main problem i have been having is it not starting on occasion. And i was hoping i would see a code for a bad cam or crank sensor, but instead the code it came back with was P0734/ Gear 4 incorrect ratio. Dammit! :mad: So i'm in the same boat as you and i am pretty much screwed.

PO734 and clicking noise ??
 

Hello. Finally someone with the same problem I have. Code PO734,clicking noise when let of gas, goes into fai safe mode and comes out of OD as soon as the engine comes up to operating temperature. No other codes. What are my options? 1. Replace transmission temperature sensor?
2. Rpl trans fluid-maybe wrong fluid put in?
3. Add trans additive in hopes it will help?
If it was either pulse generator, speed sensor, or another solenoid, wouldn't it show other codes as well? Car body is good, has only 177,000 kms on it, works like a top except OD issue, but was only a $500 car, and probably isn't worth spending big money on it I have even thought of adding a transmission cooler to try to keep trans temp down. Someone must have had this problem and was able to repair it?? Thanks in advance, Keith. Any advise will be gladly appreciated.

It could be just the input or output sensor but it's probably an internal problem with the trans. How old is the trans fluid? Is it full? I'd check on those 2 things as well.

Thanks. I already checked fluid level and it is full. I've only had the car since April so I have no idea when the fluid was changed, but it doesn't look too dirty and it doesn't smell burnt. What input and output sensors are you refering to? Thanks again.

These might help:
https://www.hyundaiforum.com/forum/h...e-0734-a-2572/
https://www.hyundaiforum.com/forum/h...ne-light-4262/
https://www.hyundaiforum.com/forum/h...734-code-6959/

I finally got that P0734 error fixed. Here's what I did
 

If P0734 appears alone, that means your transmission has internal damage. There are only 3 options:
1. replace the tranny with a used one.
2. Rebuild the tranny
3. you order some parts and DIY

The 1 and 2 option both cost more than $1500. I'm not sure my old car still worths $1500 so I opt for choice #3. After extensive reading, I think I have that overdrive clutch bearing that's exploded. Due to a faulty design, most of the P0734 failures are caused by this exploded bearing.

Luckily, it's not that difficult to fix. You don't even need to remove the transmission from the car. You need to order a new bearing kit from whatever it takes transmissions(forgot the exact URL but you can google it). The part number is 42220LK. You get a torrington race bearing, a bushing and something I can't name.

Here's the steps:
1. Jack up the car, use jackstand to support the car. remove driver side wheel.
2. Drain the transmission fluid.
3. remove all the nuts(use 12mm wrench) you find on the transmission's end cover. The top nuts can only be accessed from the top, and the only way to access them is to remove the battery, the battery tray and the air filter assembly first.
4. Use a hammer to gently hit the transmissions end cover. This will make it loose. Don't hit too hard! When it's loose, pry it open with a flat screwdriver. When the end cover fall, catch it and inside it you will find the overdrive clutch drum, and possibly the overdrive clutch itself. Note, there's a wire connecting the end cover to ECU, don't mess that up. Let the end cover hang by that wire.
5. Now, between the overdrive clutch and the Drive gear(which is the big black gear that stays in the transmission), there should be the cup race, bushing and the torrington race bearing. You may not be able to find all of them though. I didn't find my torrington bearing. It's probably already shredded to little pieces. Put the cup race on first, the cup should be facing the drive gear. Now put on the bushing, then the torrington race bearing. The little needle bearing should be facing the drive gear too.
6. Assemble the overdrive clutch and drum together, and put them in the cavity of the end cover, then fit them back into the shaft. wiggle them in and carefully attach the end cover. Make sure you align all the nut holes.
7. screw back all the nuts tight. The transmission fluid will be pressurized when the car's moving, so make sure the nuts are tight otherwise the fluid will leak. Put back the air filter assembly, battery tray and battery. Put the wheel back on. screw the transmission fluid pan nut tight(make sure it doens't leak). Lower the car.
8. Fill through the ATF dip stick. Use only SP-III compatible ATF fluid. I bought 2 gallons at advancedautoparts and they are not that expensive. $17.99 each gallon. It turned out I only need a little more than one gallon.
9. Turn on engine, step on brake, put the tranny in R, N, D, 2, L position 10 seconds each. Put back to P. Stop engine, check transmission fluid level again. Add a little if needed.
10. Test drive the car. Now the P0734 service engine soon light should be gone. The tranny should be shifting as it should(no stuck in 3rd gear anymore). Reward yourself with plenty of beer.

Total procedure takes about 4~6 hours(I did it slowly because I've never done it before, and many steps I have to figure out how to do it). On a difficulty scale 1~10(1 being easiest, like changing oil), this job is probably difficulty level 3~4.

If you can do it, congrats, you just saved yourself $1500. Cheers!

I think you deserve another beer :)

Hey Bulkwarrior,

I am experiencing the same exact issue that you described. After completing the steps that you posted, did this also eliminate the clicking noise? I have read some places that the clicking noise might be coming from the differential and is unrelated.

Thanks!

No, it doesn't get rid of the clicking noise. You have to bear with it and with time it will get fainter and fainter. I can hardly notice it now(unless I listen carefully). I think that noise is caused by shredded bearing being caught in either the torque converter or the differential. Whatever it is, it doesn't seem to hurt the car in any way, except making you worry a bit.