Here is the Wiring Diagram:
I am trying to understand how this servo motor calibration process (see screenshot of BMW software) is supposed to work at electrical level. In particular:
- there is 2-pin classification resistor attached to the servo - What does it do? Does it measure something? How to know if it is good?
- what are IMP, SM_A, SM_B, BR and DIR pins on the servo harness?
- is there a way for me to somehow test if servo motor is up to its specification by testing it outside car?
For more context, that is a transfer case servo motor (aka VTG actuator) that engages clutch pack in BMW X3 ATC400 transfer case that distributes torque between front and rear axles. Few months ago I replaced a completely worn off plastic gear (not visible in the video below) in the servo motor and was still able to calibrate it successfully. However, few days ago the car was shuddering at slow, sharp turns. So I decided to disassemble servomotor the second time to lube up the gear with grease. Now the calibration consistently fails.
I took the servo motor out of transfer box and I can see that the gear is able to spin with no load. So it is not like servo motor is completely dead. Few members on BMW forums suggested that they replaced the servo motor to solve the issue.