Merc ML320 trans speed sensor #1
Replacement of Merc transmission speed sensor for ML320 1999 with 120,000
miles. Also called a compression plate. Failure of this plate causes a
P0175 error and can cause the car to stick in one gear, usually 2nd.
If you have changed the speed sensor and the car is still stuck in 2nd gear
(called limp home mode), you must have a MB computer clear the codes.
Apparantly general code devices don't reset transmission codes.