In Failure Modes and Effects Analysis (FMEA), the AIAG-VDA handbook (2019) distinguishes between two types of controls:
- Prevention Controls – Aim to prevent the cause of failure from occurring.
- Detection Controls – Aim to identify the failure before it reaches the customer.
👉 Current Prevention Controls are considered stronger and more effective because they eliminate or reduce the probability of failure causes occurring.
They are directly linked to the Occurrence rating in FMEA.
What are Current Prevention Controls? #
- Definition: Current Prevention Controls are the measures already in place that are designed to prevent a failure cause or mechanism from occurring.
- Purpose: Reduce the likelihood of occurrence (O rating) of a failure mode.
- Focus: Proactive, aimed at design robustness, process capability, and error-proofing.
📌 Key Principle: Prevention is always stronger than detection.
Types of Current Prevention Controls #
1. Design Prevention Controls (DFMEA)
- Material selection (using higher-grade material to avoid fatigue).
- Redundant design features (dual sensors for safety-critical systems).
- Simulation & validation (CAE, FEA, durability testing).
- Compliance to standards (ISO, SAE, regulatory).
Example – DFMEA Electric Motor:
- Cause: Magnet loses strength at high temperature.
- Prevention Control: Use of high-temperature resistant rare-earth magnets.
2. Process Prevention Controls (PFMEA)
- Poka-Yoke (error-proofing devices).
- Process capability studies (Cpk, Ppk).
- Robust equipment design (auto cut-offs, interlocks).
- Preventive maintenance schedules.
- Operator training and standardized work instructions.
Example – PFMEA Bolting Process:
- Cause: Operator forgets to torque bolt.
- Prevention Control: Torque tool with auto-shutoff at correct torque.
Examples of Current Prevention Controls #
| FMEA Type | Failure Cause | Prevention Control | Occurrence Impact |
|---|---|---|---|
| DFMEA – Seatbelt | Weak buckle design | High-strength spring design validation | Reduces O rating significantly |
| PFMEA – Welding | Electrode misalignment | Fixture with poka-yoke alignment | Prevents miswelds |
| PFMEA – Painting | Paint nozzle clogging | Automatic cleaning system | Reduces defect frequency |
| DFMEA – ECU Software | Signal logic error | Software-in-the-loop testing | Prevents release of faulty code |
How Prevention Controls Influence Occurrence Rating #
- Stronger prevention controls = lower occurrence rating.
- Example:
- Without prevention → Occurrence = 8 (frequent).
- With prevention (Poka-Yoke fixture) → Occurrence reduced to 3 (rare).
👉 Occurrence ratings in FMEA must always reflect the effectiveness of current prevention controls.
Best Practices for Defining Prevention Controls #
- Always prefer prevention over detection.
- Example: Error-proofing bolt torque > sampling inspection.
- Be specific, not generic.
- Write: “Automatic torque shutoff tool” instead of “Good process design.”
- Document proven methods.
- Use historical data, SPC charts, or field experience.
- Update controls continuously.
- New technology, automation, and lessons learned must improve controls.
- Link to standards.
- Prevention controls should meet customer-specific requirements (CSRs).
Common Mistakes in Prevention Controls #
- Listing detection controls as prevention (mixing the two).
- Writing vague statements (“trained operators”) instead of actionable measures.
- Ignoring supplier or upstream controls.
- Not updating controls after process/design changes.
Case Study – PFMEA for Spot Welding #
- Function: Join two steel sheets.
- Failure Cause: Electrode wear.
- Prevention Control:
- Electrode life monitoring with automatic replacement trigger.
- Preventive maintenance every 5000 welds.
- Occurrence Rating: Reduced from 7 to 3.
👉 By focusing on prevention, the team drastically lowered defect probability.
Why Prevention Controls are Critical in FMEA #
- Directly reduce occurrence ratings.
- Strengthen process and design robustness.
- Save cost by preventing failures rather than detecting them later.
- Ensure compliance with OEM and regulatory requirements.
- Build customer trust by showing proactive risk prevention.
Key Takeaways #
- Current Prevention Controls = measures to stop failure causes before they occur.
- They directly influence Occurrence ratings in FMEA.
- Prevention is stronger than detection: error-proofing and robust design always preferred.
- Must be specific, actionable, and documented with data.
- Updating prevention controls is essential for continuous improvement.
Next Resource #
👉 Learn more about Current Detection Controls in FMEA (AIAG-VDA Standard)
