In Step 5: Risk Analysis of the AIAG-VDA 7-Step FMEA approach, once Severity, Occurrence, and Detection have been rated, the next task is to evaluate the risks.
👉 Risk Evaluation Criteria answer the question:
“Do we need to take action, or is the risk acceptable as it is?”
The AIAG-VDA standard uses Action Priority (AP) instead of the outdated Risk Priority Number (RPN) to guide these decisions.
What is Risk Evaluation in FMEA? #
- Definition: Risk evaluation is the process of interpreting the S, O, D ratings to decide whether a failure mode requires corrective action.
- Goal: Ensure that safety-critical, compliance-related, and high-impact risks are always prioritized.
- Tool: The Action Priority (AP) table provides standardized evaluation criteria.
📌 Risk evaluation does not eliminate subjectivity, but it ensures decisions are consistent, documented, and customer-focused.
Key Elements of Risk Evaluation Criteria #
1. Severity (S) – Effect-Driven
- Highest priority factor.
- Severity ≥ 9 or 10 (safety/regulatory risks) = High Priority (H), action required regardless of O or D.
- Example: Airbag fails to deploy → Severity = 10 → Always High.
2. Occurrence (O) – Cause Frequency
- Reflects likelihood of cause.
- Higher occurrence = higher Action Priority.
- Example: Bolt under-torqued found in 5% audits → Occurrence = 7 → High risk.
3. Detection (D) – Control Strength
- Reflects ability of controls to detect before customer impact.
- Weak detection (ratings 7–10) pushes AP towards High.
- Example: Visual inspection only → Detection = 8 → Weak control.
4. Action Priority (AP) – Final Decision
- Combines S, O, D into High (H), Medium (M), Low (L) priorities.
- Defines whether action is mandatory, recommended, or optional.
AIAG-VDA Risk Evaluation Categories #
| Category | Meaning | Action Guidance |
|---|---|---|
| High (H) | Unacceptable risk | Action required immediately |
| Medium (M) | Acceptable with caution | Action recommended, justify if no action taken |
| Low (L) | Acceptable risk | No action required, justification must be documented |
📌 Even Low (L) risks must be documented with justification.
Example – Risk Evaluation Using AP #
PFMEA – Bolting Operation
- Function: Secure suspension bolt at 100 ± 5 Nm.
- Failure Mode: Under-torque.
- Severity = 9 (safety-critical).
- Occurrence = 3 (rare).
- Detection = 7 (weak, manual check).
👉 AP = High Priority (H) → Action required.
Corrective Action: Introduced automatic torque monitoring → Detection improved to 2 → AP reduced to Medium (M).
Case Study – DFMEA for Electric Motor #
- Function: Provide rotation at 2000 ± 50 RPM.
- Failure Mode: Motor does not rotate.
- Severity = 8.
- Occurrence = 5.
- Detection = 6.
👉 AP = Medium (M) → Action recommended.
Decision: Team added additional insulation and motor testing.
Best Practices for Risk Evaluation in FMEA #
- Always prioritize Severity first – especially S ≥ 9 risks.
- Use real data (SPC, warranty, lessons learned) to set O ratings.
- Be realistic about Detection – manual checks = weak detection.
- Document justifications for all Medium and Low risks.
- Review AP regularly as design/process changes or controls improve.
- Involve cross-functional teams to reduce subjectivity.
Common Mistakes to Avoid #
- Still using RPN thresholds instead of AP.
- Ignoring safety risks with low occurrence values.
- Overrating manual inspections as “strong detection.”
- Failing to document why Low or Medium risks were accepted.
Why Risk Evaluation Criteria Matter #
- Ensures customer safety and compliance come first.
- Provides objective, consistent, and auditable prioritization.
- Helps allocate resources to the most critical risks.
- Strengthens trust with OEMs and auditors.
Key Takeaways #
- Risk Evaluation in FMEA = interpreting S, O, D → Action Priority (AP).
- Severity ≥ 9–10 always = High Priority, mandatory action.
- AP categories: High = action required, Medium = action recommended, Low = acceptable with justification.
- Risk evaluation ensures FMEA is a practical risk-prevention tool, not just paperwork.
Next Lesson #
👉 Continue with Lesson 3.7: Step 6 – Optimization (Actions & Re-Evaluation)
