FMEA Risk Priority Number.

RPN = Severity × Occurrence × Detection. With AIAG-VDA 2019 Action Priority (AP) — the modern method that replaced raw RPN ranking. Use for both DFMEA and PFMEA.

Severity (S) — how serious is the effect

Occurrence (O) — how often will it happen

Detection (D) — how likely will controls catch it

RPN

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Severity

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Occurrence

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Detection

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AIAG-VDA 2019 Action Priority (AP)

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RPN interpretation thresholds

RPN range	Priority	Action required
≥ 200	CRITICAL	Mandatory action — redesign or process change. Cannot ship product.
120 – 200	HIGH	Action required — develop containment plan and timeline before next phase.
60 – 120	MEDIUM	Plan corrective action — address in next continuous improvement cycle.
< 60	LOW	Monitor only — no immediate action required.
Severity = 9 or 10	SAFETY/REG	Action mandatory regardless of RPN — design out the failure mode.

What is FMEA RPN?

FMEA (Failure Mode and Effects Analysis) systematically identifies potential failures in a product or process, ranks them by risk, and drives corrective action. RPN (Risk Priority Number) is the numerical risk score:

RPN = Severity × Occurrence × Detection

Each factor is rated 1-10 per the AIAG-VDA FMEA Handbook (2019), so RPN ranges from 1 to 1000.

The Three Factors Explained

Severity (S) — How bad is the effect on the customer? 1 = no effect, 10 = injury / safety / regulatory failure.
Occurrence (O) — How often does the failure mode happen? 1 = essentially never, 10 = inevitable.
Detection (D) — How likely will the failure be caught before reaching the customer? 1 = certain detection, 10 = no detection possible.

RPN Worked Example

A bolted joint on a transmission housing.

Failure mode: Bolt loosens in service.
Effect: Oil leak, possible transmission failure → Severity = 8
Occurrence: Without anti-loosening, happens 1 in 1000 → Occurrence = 4
Current control: Visual final inspection → Detection = 7 (poor — won't catch loose internally)
RPN = 8 × 4 × 7 = 224 — HIGH RISK

Corrective action: Add Loctite or torque-angle method, plus in-process torque verification. New ratings:

S = 8 (effect unchanged), O = 1 (Loctite eliminates), D = 3 (torque tester catches)
New RPN = 8 × 1 × 3 = 24 — LOW RISK

AIAG-VDA Action Priority (AP) Method

The 2019 AIAG-VDA handbook moved away from RPN-only to Action Priority (H/M/L) based on combinations of S, O, D — not just the multiplied number. Severity 9-10 is always High Priority regardless of O and D, because safety / regulatory effects can never be left unaddressed.

RPN Interpretation Thresholds

Severity ≥ 9 — Action MANDATORY (safety / regulatory). Ignore RPN value.
RPN ≥ 200 — Critical. Redesign or replace control.
RPN 120 – 199 — High risk. Action required.
RPN 60 – 119 — Medium. Plan action.
RPN < 60 — Low. Monitor only.

Common FMEA Mistakes

Rating Severity inconsistently across team members — use the AIAG severity table.
Ignoring high-Severity / low-RPN items — Severity 9+ requires action regardless.
Treating FMEA as a one-time document — update on design change or field failure.

Related Tools

FMEA feeds directly into PPAP Element 6. Use Cp/Cpk studies to validate that your corrective action actually reduced occurrence. For inspection planning, use AQL sampling to set sample sizes proportional to risk. For cost justification, see Cost of Poor Quality.