'01 Optima Turbine Speed Sensor?

The check engine light has come on in my Optima. We took it to AutoZone and the following codes came up:

P0455 - A large leak exists in the evaporative emission control system
(From what I understand this could possibly be the gas cap? Any other possibilities?)

P0715 - A malfuction exists in the input circuit for the turbine speed sensor

I found at AutoZone I can get that sensor for $69 but we have been unable to locate it on the car?? I saw a previous thread on this with a pdf file in one of the replies but when I took that home it didn't help any as the sensor was not where it suggested it should be. Any help locating this sensor would be greatly appreciated!!!!

Evap leak can be any number of things. Common problems are with the Canister close valve.

The Input speed sensor is on top of the trans. You will have to remove the airbox to access it.

Did replacing this fix the problem? My daughter has a '01 Optima and yesterday she said she heard a thud, then the check engine light came on. I took it to Autozone and they gave me the same code of "p0715" (Input Shaft Speed Sensor System), but also "p0128" (Coolant Temp Too Low).

p0715 says it can be: faulty underdrive clutch retainer or failed input shaft speed sensor

p0128 says it can be: coolant level (good), thermostat defective (changed), ECT (Engine Coolant Temperature) sensor defective.

Can these two codes have something in common?