Common FMEA Mistakes

Customer audits, IATF assessments, and internal reviews repeatedly reveal the same weaknesses. Teams often spend significant effort completing the document while neglecting the actual risk analysis.

Generic failure modes provide little engineering value.

If the failure mode cannot be observed or measured, the team will struggle to define meaningful controls.

Many teams jump directly into failure modes without clearly defining process functions.

Weak functions create weak failure chains.

AIAG-VDA separates Prevention and Detection controls because they influence risk differently.

Mixing them together makes risk analysis less reliable.

Detection ratings are frequently too optimistic.

• Visual inspections miss defects.
• Sampling does not inspect every part.
• Measurement systems contain variation.
• Human inspectors become desensitized over time.

Overestimating inspection capability creates false confidence.

AIAG-VDA replaced RPN prioritization with Action Priority.

Modern PFMEAs should focus on Action Priority decisions.

Some organizations calculate Action Priority but never act on it.

• Assign ownership.
• Define due dates.
• Implement actions.
• Verify effectiveness.
• Re-rate risk.

AP without action management creates no real improvement.

This is one of the most common customer audit findings.

If the PFMEA identifies a critical control, the Control Plan should contain the same control.

Many PFMEAs are never reviewed after approval.

Strong organizations revisit PFMEAs after:

• Customer complaints.
• Engineering changes.
• Supplier changes.
• Tooling changes.
• Major audit findings.
• Control Plan revisions.

FMEA quality drops dramatically when a single person creates the analysis alone.

Reusing previous PFMEAs without validating assumptions creates outdated risk analysis.

Every process has unique controls, variation, tooling, operators, materials, and customer requirements.

S/O/D values without recorded justification cannot survive an audit challenge. Auditors will ask "why this number?" and a silent cell is treated as a guess.

Embed the rationale directly in the FMEA worksheet or in a linked evidence log. See the FMEA audit checklistfor the evidence auditors expect.

Occurrence is the rating most often pulled out of thin air. The AIAG-VDA scale is anchored to process capability and field history, not opinion.

See the Occurrence rating guidefor the full evidence hierarchy.

Many FMEAs list recommended actions but never re-rate after the action is implemented. Without a residual S/O/D the team cannot demonstrate that the risk actually came down.

• Severity rarely changes — only design changes reduce S.
• Occurrence drops when prevention improves (poka-yoke, capability).
• Detection drops when controls become tighter (vision, in-die sensing, 100% gauge).
• Residual AP must be recalculated using the new S/O/D.
• Effectiveness evidence (Cpk, ppm, audit) must be attached.

Every customer complaint, 8D, internal scrap event, and audit finding is a free input to the FMEA. Teams that skip this loop keep rediscovering the same failures.

The PFMEA, Process Flow Diagram, and Control Plan are a single system. When step numbering, characteristic IDs, or reaction plans drift between them, auditors immediately flag it.

• Use the same step ID across all three documents.
• Use the same characteristic ID across PFMEA and Control Plan.
• Reaction plans in the Control Plan must match the controls in the PFMEA.
• Revisions must be synchronized when any of the three changes.

See FMEA vs Control Plan for the traceability model and FMEA softwarethat enforces synchronized revisions.

• FMEA Best Practices
• FMEA Audit Checklist
• Control Plan vs FMEA
• Action Priority Guide
• FMEA Team Roles
• Worked FMEA example
• CNC machining PFMEA example
• FMEA software — built-in AP, rationale, and revision control