The SAE J1739 standard lists 3 types of controls. 1) Prevent a cause or Failure Mode, 2) Detect a Cause, 3) Detect a Failure Mode. Type 1 controls prevent, and therefore as "current" process controls have already reduced the Occurrence to the value you predict in the Occurrence column. Type 2 & 3 controls detect, and that is what is considered for the rating in the Detection column. All PM efforts reduce Occurrence. If there were no other controls, then there would be no detection and the Detection rating would be 10.