2002 Sonata internittent check engine light and won't shift

every now and then the check engine lite will come on and the car will shift into 2nd or 3rd and stay in that gear and will not automatically **** on its own, you can manually shift between 2nd and 3rd.  If you shut the car off most of the time the transmission will start to function perfect but usually the check engne lite will stay on for some time. Some times for a day or two or sometimes only for a few minutes. Sometimes the transmission will start to function properly on its own while you are driving as wll. Sometime I can drive a week without a problem andsometimes it happens 2 or 3 times in a day. Temp also does not seem to be a factor.  I have had it in a local shop sveral times and they keep reading the same two codes ( 0720 and 1520 or 1529) They have called the nearest dealer and they claim that these codes shouldn't cause this problem.  The car is going back into the shop in a couple of days. any help would be greatly apprecated. the car has 103000 km

Hello New Member Thumper..
New to me so when the dealer ever finds out and tell you, come back in and post the answer for everyone in case someone else gets the same problem..
 
                                       WheelBroker1

Hi Thumper,
 
I also have a 2002 Sonata and although I am not getting an engine check light, I do find that occaisionaly, usually when cold, it sticks in second, but as soon as I change manually it then operates perfectly, so I would be interested to find out what the problem is too.
 
Chris.

Almost sounds like a shift select switch issue.  That or a speed sensor is going bad.

I also have the same problem with a 2000. I replaced the input and out speed sensors and still have the problem. Any ideas what else I can replace to correct this issue.
 
Thanks

Note that there are several sensors for the AT, including the vehicle speed sensor, the A and B pulse generators and the throttle position sensor.  If any of these are malfunctioning, it could cause the AT to go into "limp home mode" where it doesn't change gears.  This is because it is getting a gross error between how fast the motor is spinning, how fast the wheels are spinning, and/or the throttle position.


DESCRIPTION:
An improperly functioning input speed sensor or output speed sensor on a 1999-2001 Sonata, 2001 Elantra, 2001 Santa Fe and 2001 XG300 may result in the following conditions:

1. Harsh P-R or P-D engagement shock
2. Transaxle allows acceleration in 1st gear to 5000 rpm, then shifts into 3rd gear fail-safe
3. Check Engine light on
4. Diagnostic trouble codes:

P0715 (no input speed sensor signal - open/short)
P0720 (no output speed sensor signal - open/short)
P1529 (TCM MIL request to ECM)
 
REPAIR PROCEDURE:
1. Check for DTCs in both the Engineand Automatic Transaxle menus. If you find:
P0715, Replace input speed sensor
P0720, Replace output speed sensor
P1529, Erase code


2. Drive the vehicle for at least two key-on to key-off driving cycles. If the codes do not reset, return the vehicle to the customer. If P0715 or P0720 return, go to step 3.
3. Use a DVOM to check the resistance of the wiring between the TCM and the input sensors and output sensors. If the resistance is:
More than 1 ohm, repair or replace the wiring harness
Less than 1 ohm, go to Step 4.
4. Replace the transaxle control module (TCM).

PARTS INFORMATION:
MODEL- 1999-2001 Sonata, 2001 Elantra, 2001 Santa Fe, 2001 XG300

Input Speed Sensor:  42620-39051

Output Speed Sensor:  42621-39052