2000 Sonata drops to third gear and stays there until I restart the engine.

I've been having this trouble for some time now. I could be driving at
any speed when the transmission will drop down a gear and stay there.
If I restart the engine the tranny will shift properly until this
problem reoccurs. I have codes too. P1529, I have no idea what that one
is, I was told it is a manufacturer specific code. P0720 "The PCM has
determined that a malfunction exists in the electrical circuit for the
output speed sensor" . P0715 "The PCM has determined that a malfunction
exists in the input circuit for the turbine speed sensor." Please help
this is driving me insane.

 

Sounds like you have a problem with a speed sensor and this is confusing
your transmissions control computer. Take it to a competent garage and
get it fixed.


Matt

 

P1529 is simply an indicator that the transmission computer requested the
check engine lamp. Your descriptions for P0715 and P0720 are correct.

In nearly every instance when I've seen P0715 or P0720, the problem has
been with the sensor. I'd recommend replacing both the input speed sensor
and the output speed sensor. Chances are this will take care of the entire
problem.