FMEA - Reduced D Ranking by Use of Preventative Maintenance

Dear forum
I have a question about PFMEA. In FMEA manual published by AIAG, reduced "D" ranking by use "Preventative Maintenace". But in their instruction wrote that "preventative action" can reduce "O" ranking. Which is correct?

[Kevin Mader]

Interesting observation.

Is Prevention....Detection? By many standards, no.

By the usage in the FMEA, they associate Detection ratings with Current Process Controls (see the FMEA worksheet). As such, it will influence your D rating.

Occurence ratings are associated with the Process control. How often will a failure Mode occur if your Process Control is in place and functioning properly? As such, it also influences the O rating.

Perhaps both is the right answer. Anyone out there with more thought on this?

Back to the group...

Kevin

[Marc]

Dear Behrooz:

You're just trying to confuse us, yes??

Like Kevin said: If you increase preventive maintenance, it's (if it works - increasing PM is not always going to reduce failures) going to reduce the probability that the equipment will fail - thus reducing the Occurance rating.

[This message has been edited by Marc Smith (edited 03 July 2000).]

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.