FMEA Risk Scoring: RPN vs. Action Priority (AP) under AIAG-VDA

If you learned FMEA the old way, you ranked risk with RPN — Risk Priority Number. The current AIAG-VDA FMEA handbook moved away from that to Action Priority (AP). If your customers expect AIAG-VDA FMEAs and you're still sorting by RPN, this is the gap to close.

This builds on the IATF 16949 core tools overview.

The old way: RPN

RPN multiplies three 1–10 ratings:

RPN = Severity × Occurrence × Detection

You'd then chase the highest numbers. The problem is that multiplication hides risk. An RPN of 100 could be 10×10×1 (a catastrophic, frequent failure you happen to detect well) or 4×5×5 (a moderate one) — same number, completely different urgency. Worse, teams set arbitrary RPN "thresholds" (e.g., act on anything over 100), which let genuinely dangerous, high-severity items slip through if their product happened to land low.

The new way: Action Priority (AP)

AIAG-VDA keeps the same three 1–10 scales — Severity (S), Occurrence (O), Detection (D) — but instead of multiplying them, it uses a lookup table that returns an Action Priority of High, Medium, or Low.

The table is deliberately weighted toward Severity first, then Occurrence, then Detection. So:

• High S + high O → High AP, regardless of how good detection is. You can't "inspect your way out" of a severe, frequent failure.
• Low-severity, rare items land at Low AP.

AP tells you where to focus action, not a score to optimize. It's a priority for action, not a pass/fail gate.

How to score the current way

1. Build the FMEA structure (function → failure mode → effect → cause → controls).
2. Rate Severity of the effect (1–10).
3. Rate Occurrence of the cause (1–10).
4. Rate Detection of the current controls (1–10).
5. Look up S/O/D in the AP table to get High / Medium / Low.
6. Prioritize and document action on High first, then Medium. Low generally needs no action beyond justification.
7. Re-evaluate S/O/D after actions are taken.

Practical notes

• Don't keep ranking by RPN in an AIAG-VDA FMEA — customers and auditors expect AP.
• Severity ratings come from effects, not causes — a frequent miswrite.
• AP isn't a threshold game. The point is to force attention onto high-severity risks that RPN math used to bury.

A tool helps here because the AP lookup is fixed logic: enter S, O, and D and the priority is determined for you, consistently, every time — with the FMEA linked to the control plan so actions actually flow downstream. That's how GatesFlow FMEA software handles it: AIAG-VDA structure, automatic AP, and a direct link into control plans and PPAP.

Switching from RPN to AP isn't just a relabel — it changes what your team works on, and it puts severity back where it belongs: first.