In Failure Modes and Effects Analysis (FMEA), the AIAG-VDA handbook defines two types of controls:
- Prevention Controls → Prevent the cause of failure from occurring.
- Detection Controls → Identify the failure cause or mode if it occurs, before it reaches the customer.
👉 Current Detection Controls focus on identifying failures, not preventing them. They determine the Detection (D) rating in FMEA.
What are Current Detection Controls? #
- Definition: Current Detection Controls are the methods, inspections, or tests already in place to discover causes or failure modes before the product reaches the customer.
- Purpose: Reduce the probability that a failure will escape undetected.
- Focus: Verification, testing, inspections, monitoring, audits.
📌 Key Rule: Detection does not prevent a failure — it only improves the chance of catching it.
Types of Current Detection Controls #
1. Design Detection Controls (DFMEA)
- Design verification tests.
- Durability & reliability tests.
- Simulation (CAE, FEA, software-in-the-loop).
- Prototype evaluations.
Example – DFMEA Electric Motor:
- Failure Mode: Winding short circuit.
- Detection Control: High-voltage insulation test on prototype.
2. Process Detection Controls (PFMEA)
- In-process inspections (visual checks, dimensional checks).
- Statistical Process Control (SPC) with alarms.
- 100% automated checks (sensors, gauges).
- End-of-line testing (functional, leak test, torque test).
- Audits and sampling plans.
Example – PFMEA Bolting Process:
- Failure Mode: Under-torque bolt.
- Detection Control: Digital torque monitoring system with alarms.
Examples of Current Detection Controls #
| FMEA Type | Failure Mode | Detection Control | Detection Rating Impact |
|---|---|---|---|
| DFMEA – ECU Software | Logic error | Automated diagnostic self-test | Rating 2 (almost certain detection) |
| PFMEA – Welding | Weld nugget missing | Visual inspection by operator | Rating 7–8 (weak detection) |
| PFMEA – Painting | Thin coating | Random thickness sampling | Rating 6 (moderate detection) |
| DFMEA – Brake System | Sensor signal error | Hardware-in-loop testing | Rating 3 (very reliable detection) |
📌 Strong detection controls (error-proofing, 100% automated tests) = low Detection rating (1–3).
📌 Weak detection controls (manual checks, random audits) = high Detection rating (7–10).
How Detection Controls Influence FMEA #
- Detection ratings are not about preventing failures — they only measure how well current methods catch failures before release.
- Example:
- Visual check of bolts → Detection = 7 (weak).
- Automatic torque verification → Detection = 2 (strong).
👉 Better detection controls → lower Detection rating → improved Action Priority (AP).
Best Practices for Current Detection Controls #
- Be realistic: Manual inspection is weak, rarely better than D=6–7.
- Prefer automation: Sensors, alarms, error-proofing are far more reliable (D=1–3).
- Document detection methods clearly: Who checks, how, and at what frequency.
- Validate detection effectiveness: Use MSA (Measurement System Analysis) and calibration.
- Link to control plans: In PFMEA, ensure detection methods align with process control plans.
- Update controls: After adding new technology, re-evaluate Detection ratings.
Common Mistakes in Detection Controls #
- Treating detection as prevention (they are not the same).
- Overestimating manual inspections → assuming operators will always catch defects.
- Copying detection ratings from past FMEAs without validation.
- Not documenting evidence of effectiveness (no calibration, no audits).
Case Study – PFMEA for Painting Process #
- Function: Apply protective coating.
- Failure Mode: Coating thickness too thin.
- Current Detection Control: Random sampling with micrometer → Detection rating = 6.
- Improvement: Automated coating thickness measurement (100% check) → New rating = 2.
👉 Result: Risk reduced significantly because failures can be detected before delivery.
Why Detection Controls are Important in FMEA #
- They determine how much uncontrolled risk reaches the customer.
- They drive Detection rating (D) in FMEA → critical for Action Priority.
- They highlight where process improvements (automation, sensors, poka-yoke) are needed.
- They ensure compliance with IATF 16949 and OEM requirements for robust quality control.
Key Takeaways #
- Current Detection Controls = methods to discover failures before they escape.
- Strong detection = low Detection rating (1–3). Weak detection = high rating (7–10).
- Always document detection controls in detail.
- Detection reduces risk but does not replace prevention — prevention is always stronger.
- Updating detection methods improves FMEA credibility and reduces risk priority.
Next Resource #
👉 Learn more about FMEA Optimization – Step 6 in AIAG-VDA Approach
