AIAG & VDA FMEA

This section is the library reference for the Derisker AIAG & VDA FMEA SysML v2 library, based on the AIAG & VDA FMEA Handbook (1st Edition 2019, 2nd Printing 2022). The library currently supports Design FMEA (DFMEA). Process FMEA (PFMEA) and FMEA-MSR support is planned.

The AIAG & VDA FMEA Handbook harmonises the previously separate AIAG (USA) and VDA (Germany) approaches into a single, globally accepted automotive risk analysis methodology. It introduces a structured 7-step process (System Analysis → Failure Analysis & Risk Mitigation → Risk Communication) and replaces the Risk Priority Number (RPN) with Action Priority (AP), a three-level system (H, M, L) derived from Severity, Occurrence, and Detection ratings.

For step-by-step modelling guidance, see AIAG & VDA FMEA: Design FMEA. For a complete worked example, see Electric Vehicle DFMEA.

Quick Reference

Library Types

Type	Package	Purpose
FMEA_Design	DFMEA	Analysis def for a DFMEA (7-step process); use as analysis myDFMEA : FMEA_Design
DFMEA_Header	DFMEA	Header metadata (company, dates, team, FMEA ID, etc.)
FailureMode	DFMEA	Occurrence def for a failure mode at any hierarchy level; includes FEs, S, FCs, O, D, AP, prevention controls (control methods that reduce occurrence), detection controls, and Step 6 fields
Causation_FM_FC	DFMEA	Connection linking a lower-level cause FM to an enclosing effect FM
#failureMode	DFMEA	Metadata keyword — declares a FailureMode inside a function; auto-collects into FMs
#failureCause	DFMEA	Metadata keyword — declares a Causation_FM_FC inside a failure mode
Pdiagram	DFMEA	Metadata def for P-diagram annotation on functions (control factors, noise factors)
Function_AIAG_VDA_FMEA	DFMEA	Abstract action def that provides the FMs collection; every function used in a DFMEA must specialize this

Rating Enumerations

Type	Package	Purpose
SR	DFMEA	Severity rating enum (S1_VeryLow – S10_VeryHigh, Sx_Inherited)
OR	DFMEA	Occurrence rating enum (O1_ExtremelLow – O10_ExtremelyHigh, Ox_Inherited)
DR	DFMEA	Detection rating enum (D1_VeryHigh – D10_VeryLow, Dx_Inherited)
APR	DFMEA	Action Priority enum (H, M, L, TBD)
FMType	DFMEA	Failure mode type enum (see below)
Status	DFMEA	Optimization status enum (open, decisionPending, implementationPending, completed, notImplemented)
Confidentiality	DFMEA	Confidentiality level enum for the DFMEA header

Calculation Functions

Calc Def	Purpose
CalcAP	Computes Action Priority (AP) from S, O, D; called automatically
InheritSeverityRating	Returns Sx_Inherited — severity inherited from FEs.S.value
InheritOccurrenceRating	Returns worst-case O from all failure causes; used on non-leaf FMs
InheritDetectionRating	Returns worst-case D from all failure causes; used on non-leaf FMs
InheritOccurrenceRatingOfFC	Returns inherited O for a Causation_FM_FC connection; applied automatically
InheritDetectionRatingOfFC	Returns inherited D for a Causation_FM_FC connection; applied automatically

File Layout

models/aiag_vda_fmea/
├── lib/
│   └── Derisker_AIAG_VDA_FMEA.sysml          # Core library (ratings, FM defs, AP calc)
├── examples/
│   └── dfmea/
│       └── Example_DFMEA_ElectricVeh.sysml    # Electric Vehicle DFMEA example
└── README.md

Severity Ratings (S)

Enum	Level	Effect on End User
S10_VeryHigh	Very High	Affects safe operation of vehicle; potential injury
S9_VeryHigh	Very High	Noncompliance with regulation / legislation
S8_High	High	Loss of primary function during service life
S7_High	High	Degradation of primary function during service life
S6_Moderate	Moderate	Loss of secondary function during service life
S5_Moderate	Moderate	Degradation of secondary function during service life
S4_Moderate	Moderate	Very objectionable NVH (Noise, Vibration, Harshness)
S3_Low	Low	Moderately objectionable NVH
S2_Low	Low	Slightly objectionable NVH
S1_VeryLow	Very Low	No discernible effect on vehicle operation
Sx_Inherited	—	Marker for inherited severity; do not set manually — use InheritSeverityRating

Occurrence Ratings (O)

Enum	Level	Typical Failure Rate
O10_ExtremelyHigh	Extremely High	≥ 1 in 10
O9_VeryHigh	Very High	1 in 20
O8_VeryHigh	Very High	1 in 50
O7_High	High	1 in 100
O6_High	High	1 in 500
O5_Moderate	Moderate	1 in 2,000
O4_Moderate	Moderate	1 in 10,000
O3_Low	Low	1 in 100,000
O2_Low	Low	≤ 1 in 1,000,000
O1_ExtremelyLow	Extremely Low	Eliminated by design
Ox_Inherited	—	Marker for inherited occurrence; do not set manually — use InheritOccurrenceRating

Detection Ratings (D)

Enum	Level	Detection Control Maturity
D10_VeryLow	Very Low	No detection method defined
D9_VeryLow	Very Low	Detection method not designed for this failure mode
D8_Low	Low	New, unproven detection method
D7_Low	Low	New method; pass/fail only, no design-improvement time
D6_Moderate	Moderate	Proven method; later in development cycle
D5_Moderate	Moderate	Proven method; degradation testing
D4_High	High	Proven method; sufficient time for design improvement
D3_High	High	Proven method; test-to-failure
D2_High	High	Proven method; degradation testing; early in development
D1_VeryHigh	Very High	Failure mode cannot physically occur as designed
Dx_Inherited	—	Marker for inherited detection; do not set manually — use InheritDetectionRating

Action Priority (AP)

AP is computed automatically from S, O, D via CalcAP. Do not set it manually. AP has only three values — there is no “N/A” (per AIAG & VDA errata, June 2020).

AP	Meaning	Action Required
H	High priority	Actions required — failure must be addressed before release
M	Medium priority	Actions recommended — engineering team should evaluate
L	Low priority	Actions optional — may be addressed at team discretion
TBD	Ratings incomplete	Complete S, O, and D ratings; AP will be calculated automatically

AP weighting: Severity dominates (a high S drives AP up regardless of O and D), then Occurrence, then Detection. This prevents low-severity items from consuming resources.

Failure Mode Type (FMType)

Enum Value	Meaning
FMType::lossOfFunction	Complete failure — function stops entirely
FMType::degradationOfFunction	Reduced performance over time
FMType::intermittentFunction	On/off behaviour — function works sometimes
FMType::partialFunction	Partial performance loss
FMType::unintendedFunction	Function activates when it should not
FMType::exceeedingFunction	Function operates above intended threshold
FMType::delayedFunction	Function activates after an unintended delay

S, O, D Assignment Rules

Rating inheritance is handled by library calculation functions. The rules depend on the FM’s role in the failure chain, not on a fixed level number.

FM Role	Severity (S)	Occurrence (O)	Detection (D)
Top-level (FEs = (), no effects above)	Set manually, e.g. SR::S8_High	InheritOccurrenceRating(FCs.O.value)	InheritDetectionRating(FCs.D.value)
Intermediate (has effects above and causes below)	InheritSeverityRating(FEs.S.value)	InheritOccurrenceRating(FCs.O.value)	InheritDetectionRating(FCs.D.value)
Leaf (has effects above, no causes below)	InheritSeverityRating(FEs.S.value)	Actual rating, e.g. OR::O4_Moderate	Actual rating, e.g. DR::D4_High

Special cases:

• No higher-level effect — if an FM has FEs = () and its end-user impact is negligible (e.g. S1), severity can be assigned directly at any level.

• Terminal intermediate FM — an FM at any intermediate level that deliberately has no causes decomposed below it acts as a leaf; assign direct O and D ratings.

• Failure cause O/D — InheritOccurrenceRatingOfFC() and InheritDetectionRatingOfFC() are applied to Causation_FM_FC connections automatically; do not set them in the model.

How the Failure Chain Works

LVL0 System FM  ──(caused by)──>  LVL1 Subsystem FM  ──(caused by)──>  LVL2 Component FM
   S set here                        S inherited (calc)                    S inherited (calc)
   O,D inherited (calc)              O,D inherited (calc)                  O,D set here

• Severity propagates downward — set once at LVL0, inherited by all lower FMs via InheritSeverityRating(FEs.S.value).

• O and D aggregate upward — actual values at the lowest level, worst-case propagated up via InheritOccurrenceRating() / InheritDetectionRating().

• Every node is a FailureMode — whether it acts as “effect”, “mode”, or “cause” depends on perspective.

• Multiple causes can feed one FM (OR logic — any cause can trigger the effect).

• FEs (failureEffects) — each FM’s ref occurrence :>> FEs records the higher-level FM(s) it feeds into. LVL0 FMs use FEs = () (no higher level). Shared FMs use tuple syntax: FEs = (effectA, effectB).

• FE path convention — paths always navigate from the top-level system design package qualifier (e.g. LVL0::EV::), then dot-access: LVL0::EV::function.fm for LVL1 FMs, LVL0::EV::subsystemPart.function.fm for LVL2 FMs.

• Optimization updates — when a Step 6 action improves O or D at the leaf level, update the actual rating directly on the leaf FM; inheritance calculations propagate the change upward automatically.