After defining functions and requirements in Step 3, the next step in the AIAG-VDA 7-Step FMEA methodology is Failure Analysis.
👉 Failure Analysis answers three essential questions:
- How can the function fail? (Failure Mode)
- What happens if it fails? (Failure Effect)
- Why does it fail? (Failure Cause)
This structured approach helps teams identify potential risks systematically, ensuring no critical failures are overlooked.
1. What is a Failure Mode in FMEA? #
A Failure Mode describes how a function fails to meet its requirement.
- It is the deviation from intended function or requirement.
- A failure mode should always be specific and observable.
Examples of Failure Modes
- DFMEA (Design):
- Motor winding open circuit.
- Seatbelt webbing tears under load.
- PFMEA (Process):
- Weld not formed.
- Bolt under-torqued.
📌 Tip: Write failure modes as “Does not…” or “Exceeds…” the requirement.
2. What is a Failure Effect in FMEA? #
A Failure Effect is the consequence of the failure mode on the next higher level, the end user, or the customer.
- Effects can be local, next-level, or end-user/customer impacts.
Examples of Failure Effects
- DFMEA (Motor Winding Open Circuit):
- Local: Motor loses torque.
- End-user: Vehicle cannot start.
- PFMEA (Weld Not Formed):
- Local: Assembly weak.
- End-user: Component breaks during vehicle use.
📌 Severity in FMEA is always linked to the effect.
3. What is a Failure Cause in FMEA? #
A Failure Cause explains why the failure mode occurs.
- Causes are linked to design weaknesses, process variation, or human errors.
- Each cause must be something the team can act upon to reduce risk.
Examples of Failure Causes
- DFMEA (Motor Winding Open Circuit):
- Cause: Insulation breakdown due to overheating.
- PFMEA (Bolt Under-Torqued):
- Cause: Torque wrench not calibrated.
📌 Tip: Causes should be written in terms of root causes, not vague descriptions like “bad part.”
Relationship Between Failure Mode, Effect, and Cause #
Function → Requirement → Failure Mode → Failure Effect → Failure Cause
👉 Example – PFMEA Bolting Process
- Function: Secure bolt at 100 ± 5 Nm.
- Requirement: Torque between 95–105 Nm.
- Failure Mode: Under-torque (<95 Nm).
- Failure Effect: Bolt loosens during driving.
- Failure Cause: Torque wrench calibration drift.
Example – DFMEA for Electric Motor #
- Function: Provide rotation at 2000 ± 50 RPM.
- Failure Mode: Motor rotates at <1500 RPM.
- Failure Effect: Reduced vehicle acceleration.
- Failure Cause: Magnet strength below specification.
Why Failure Analysis is Important #
- Systematic Risk Identification: Ensures no failure paths are missed.
- Customer Safety & Satisfaction: Effects show real-world impact.
- Root Cause Focus: Causes allow teams to define prevention actions.
- Foundation for Risk Analysis: Severity, Occurrence, and Detection ratings are all based on these elements.
Common Mistakes in Failure Analysis #
- Writing vague failure modes (“not working” instead of “open circuit in winding”).
- Confusing failure mode with failure effect (mixing “how it fails” with “what happens”).
- Listing generic causes (“human error”) instead of specific, actionable causes.
- Skipping next-level or customer effects → underestimating risk severity.
Case Study – PFMEA for Welding Process #
- Function: Join two steel sheets by spot welding.
- Requirement: Weld strength ≥ 5 kN.
- Failure Mode: Weak weld (<3 kN).
- Failure Effect: Component detaches under vibration (Severity = 9).
- Failure Cause: Electrode wear causing poor heat transfer.
👉 Because the mode, effect, and cause were clearly defined, the team implemented electrode monitoring and maintenance schedules, reducing risks significantly.
Key Takeaways #
- Failure Mode = How function fails.
- Failure Effect = What happens if it fails.
- Failure Cause = Why it fails.
- Together, these form the core of FMEA risk analysis.
- A well-structured Failure Analysis ensures accurate Severity, Occurrence, and Detection ratings.
Next Lesson #
👉 Continue with Lesson 3.5.1: Failure at Function Level → Failure Modes
