I'm having a problem with my '00 Sonata downshifting to 3rd at highway speeds. Getting the following trouble codes:

P0715: Input/Turbine Speed Sensor Circuit Malfunction
P0740: torque convertor clutch solenoid circuit
P0705: Range switch signal incorrect

The downshifting problem is intermittent and when it happens it seems that only 2nd and 3rd gear are available. Pulling over, shutting the car off and restarting restores normal operation.

My question is this: Should I try replacing the sensors first? I've done some research and seen this downshifting problem attributed to both the Input Speed Sensor and the Range Switch. I've also seen a recommendation to simply flusg the AT fluid. I've also read that Hyundai recommends Transaxle replacement for P0740. Can anyone confirm this?

this problem is not uncommon, l would drain and refill the trans (use SP111 fluid) and change the input and output speed sensors, this would normally cure the problem if not you may have internal problems in the trans

Dear Soul,

Yes, concur with Montego, your transmittion symptoms are now a definite trend for 2000 and 2001 Sonatas. the course of action is correct, choosing cheap fixes first.

1) Transmission fluid exchange with SP-III fluid. Not work?
2) Change the input and output sensors on the transmission. Not work?
3) Have your throttle position sensor checked. this is the expensive one, so don't replace unless it confirms as bad.

Of course, Hyundai recommends you replace the transmission for 0740. If you listen to a service writer long enough, he will recommend replacing the car too. The clutch solenoid circuit can be rebuilt, but this requires a complete transmission rebuild. Current pricing in Colorado for this is a range from $1,400 to $2,000. If you can not eliminate the symptoms with the steps above, you will have to ask the hard question of when do you 'pull the plug' on this car. Try checking your current market price in Kelly Blue Book (kbb.com) and remember that this may just the start of high mileage/high wear problems on your Sonata. I have 110K miles on mine, and not expecting much beyond 160k miles.

Byron

Wow, thanks for the prompt replies! The output speed sensor was replaced about 3 years ago. Think it's still necessary to change both input and output sensors? Or is it one of those things that should always be done at the same time?

alot depends on the mileage, has the trans. fluid been changed at regular service intervals?...you could try it step by step, change the fluid first if no difference change one speed sensor and so on