Diagnostic System Check - Automatic Day - Night Mirror

A Diagnostic System Check - Automatic Day-Night Mirror:

TEST DESCRIPTION
The number(s) below refer to the step number(s) on the diagnostic table.
2. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit:
4. If class 2 communication is lost, the module will set U" codes for the loss of communication.