The transmission has two speed sensors, an input speed sensor and an
output speed sensor.  The computer checks the ratio of the input sensor
and output sensor and checks to see if this agrees with the gear as
reported by the PNP switch.

A fault can be created by a failure of any of these 3 components.

The error code was incorrect speed ratio.  I had a bad pnp switch but
the dealer replaced the 2 speed sensors first.  That is expensive
troubleshooting.