which sensor do you change, due to 4wd problem

It was serviced at 70k miles with same problem, had sensor changed but cant remember which one, dont think its the motor just sensor. Dont want to buy all 3 sensors

thanks for replies ; am planning on doing that ,having codes read; was just asking if anyone knew off hand as there is a parts number per sensor

It is most likely NOT a sensor of any kind. The reason for the scan is to know what the problem actually is, anything else is just guessing!