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FMEA Prevention and Detection Controls: A Reference List with Examples

The current controls columns are where FMEA ratings often become wishful. This list separates prevention controls, which reduce the chance the cause occurs, from detection controls, which find the cause or failure mode before it reaches the customer, and states the weakness of each.

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Control type	Control	What it addresses	Example	Limitation to rate honestly
Prevention	Poka-yoke, physical keying	Wrong part, wrong orientation	Asymmetric fixture pin so the part only fits one way	Can be defeated if operators bypass or force the part
Prevention	Poka-yoke, sensor interlock	Missing component or step	Presence sensor blocks cycle start if a clip is absent	Sensor drift or bypass keys reduce the effect
Prevention	Preventive maintenance schedule	Wear-related cause	Scheduled stencil or nozzle replacement by cycle count	Interval must be based on data, not habit
Prevention	Tool life management	Dimension drift from tool wear	CNC tool counter forces change after set parts	Counter must be reset and actually enforced
Prevention	Error-proof recipe download	Wrong program or parameters	Parameters loaded from controlled system, not typed	Depends on revision control of the source
Prevention	Statistical process control with reaction plan	Process drift before nonconformance	X-bar and R chart with stop rules at the machine	Only prevents when someone reacts to signals
Prevention	Torque tool with count and angle control	Under or over torque	Controller counts fasteners and locks until all are done	Needs calibration and joint-specific limits
Prevention	Kitting and line-side bin control	Mixed or wrong parts	Kitted components per work order with barcode check	Kit errors move upstream rather than disappear
Prevention	Controlled work instructions with visual aids	Operator method variation	Photo-based instruction at the station	Weak alone; relies on operator discipline
Prevention	Operator training and certification	Skill-related cause	Skills matrix with sign-off before solo work	Rate as weak prevention for high-severity items
Prevention	Supplier certification and material approval	Incoming material variation	Approved supplier list with certificate of conformance	Certificate accuracy is trust, not verification
Prevention	Environmental control	Contamination, humidity, ESD	Cleanroom class, humidity logging, ESD flooring	Needs monitoring and alarm response
Prevention	Design margin or design rule	Design cause in DFMEA	Derating rule, minimum wall thickness rule	Rules must be applied and reviewed
Prevention	First-piece approval after setup	Setup error	Setter and inspector sign-off before release to run	Detects setup error but not later drift
Detection	In-process automated gauging	Dimensional failure mode	In-machine probe measures bore after cut	Probe calibration and measurement uncertainty
Detection	Automated optical inspection	Missing, misplaced, bridged parts	AOI after reflow	False calls and programmed coverage limits
Detection	Vision system with golden image	Presence, orientation, label	Camera verifies label text and position	Lighting and part variation affect reliability
Detection	End-of-line functional test	Function failure	Powered test against specification	Only tests what the test program covers
Detection	Leak test	Seal or weld leak	Pressure decay or helium test	Sensitivity set by test parameters
Detection	Continuity and hipot test	Wiring errors, insulation faults	Cable harness tester after assembly	Does not find latent defects such as weak crimps
Detection	Go and no-go gauge	Hole or thread size	Thread plug gauge at the station	Operator dependent; wear of gauge itself
Detection	CMM inspection per sample plan	Critical dimensions	Periodic CMM check of key features	Sampling can miss intermittent failures
Detection	Visual inspection by operator	Cosmetic and gross defects	Final visual check with defect samples	Rate detection poorly for rare or subtle defects
Detection	Torque audit by sampling	Fastener torque	Audit wrench check on a sample of assemblies	Sampling only; detects after the fact
Detection	Barcode scan verification	Wrong part or label	Scan component and work order match before use	Detects mismatch only if label is correct
Detection	Dimensional or material certification review	Incoming material	Receiving inspection against certificate and sample test	Sample size and test method limit coverage
Detection	Burn-in or environmental stress screening	Infant mortality	Temperature cycling before shipment	Cost and time; screens only certain failure types
Detection	Customer or field feedback loop	Escapes	Warranty data reviewed monthly	Late detection; not a manufacturing control

In the AIAG-VDA method, prevention controls support the occurrence rating and detection controls support the detection rating. Rate a control on its demonstrated effectiveness, not on its mere existence.

Link inspection plans to your FMEA

Optional: a short review of how routings, inspection plans and NCR data in your ERP could feed FMEA controls.

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Prevention versus detection

A prevention control acts on the cause: a sensor interlock, a keyed fixture or a tool-life counter lowers the likelihood that the failure mode occurs at all, so it supports the occurrence rating. A detection control finds the cause or failure mode after it exists, such as an end-of-line test or an AOI station, so it supports the detection rating. The same activity can be one or the other depending on where it sits. An SPC chart with an enforced reaction plan prevents; a chart nobody reads detects nothing.

How to use the list

Search for the failure mode or the cause you are analysing, then pick controls that really exist on your line. Write the control in your FMEA with its specifics: what is checked, with what gauge, at what frequency and who reacts. Avoid listing training as a strong control for a high-severity item. Then move to the limitation column and ask whether that weakness applies here, and whether it should push the rating up.

List only controls that already exist when you rate; planned ones belong in recommended actions
Name the gauge, frequency and reaction for every detection control
Match each control to a cause, not just to the failure mode
Carry the same controls through to the control plan

Common mistakes

The most common error is giving full credit to a control that is bypassed in practice, or counting a sampling inspection as if it screened every part. Another is rating detection low because a test exists, when the test cannot see the specific failure mode. Check each detection control against the failure mode: can it actually distinguish good from bad for this characteristic, at this stage, before the part leaves your control? Where the honest answer is not yet, rate it that way and add an action.

Frequently Asked Questions

Does a detection control reduce occurrence?

No. A detection control finds a problem that has already occurred, so it improves the detection rating only. Only a prevention control that acts on the cause should be used to justify a lower occurrence rating.

Is operator training a valid control?

It counts, but it is generally a weak prevention control because it depends on human consistency. For high-severity effects, teams should look for error-proofing or automatic checks rather than relying on training alone.

Should the same control appear in the control plan?

Yes. The controls you rely on in the FMEA should appear in the control plan with specification, measurement method, sample size, frequency and reaction plan. A control that is in the FMEA but not in the plan is not really controlled.

Is a sampling inspection a good detection control?

Only for failure modes that are consistent across a lot. For random or intermittent failures a sample can miss them entirely, so detection should be rated with that gap in mind.

If you want control plan methods, gauges and reaction plans traced from your ERP routings and inspection plans, we can discuss how that data could be read in place.

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