Hi,

I have a 2005 Hyundai Sonata with a V6 where my engine check light came on and so I checked for what code was on the computer and found the P0121. The issue I'm having is that my automatic transmission will not shift in drive now and I have to manually shift the gears. There are no other codes coming up and the transmission jerks into gear when I go from park to reverse or park to drive. Once in awhile the idle fluctuates but there are no other negative symptoms. Would a throttle position sensor fault create the issue with the transmission?

 

Your vehicle has "Electronic Throttle Control" and has 2 sensors A & B which constantly cross check one another to assure proper throttle operation and control.

The code you posted indicates there is a problem with the "A" sensor. It could be a questionable connection or the sensor itself. A scan tool will confirm if the sensor is defective, or if you choose you might read up on the system and if confirmed replace the sensor itself.