Why AIAG-VDA Changed FMEA
Traditional FMEA methods used Risk Priority Number (RPN) — a simple multiplication of Severity × Occurrence × Detection ratings. The problem? RPN treats a catastrophic failure that rarely occurs (S=10, O=2, D=5, RPN=100) the same as a minor annoyance that happens constantly (S=2, O=10, D=5, RPN=100). The AIAG-VDA standard replaced RPN with Action Priority (AP), a categorical classification system that prioritizes severity first, then considers occurrence and detection.
The AP Decision Logic:
This categorical approach ensures that high-severity failures always receive high priority, regardless of how rare they might be. TestAuto2 implements this logic as a JavaScript formula in its FMEA risksheet configurations, automatically calculating both pre-mitigation and post-mitigation AP values.
The Seven-Step FMEA Process
AIAG-VDA defines a structured seven-step methodology for conducting FMEA. TestAuto2 encodes this process through nine progressive workflow views in its risksheet configurations, revealing columns only when users reach the appropriate analysis stage:
| Step | AIAG-VDA Activity | TestAuto2 View | Visible Columns |
|---|
| 1 | Planning and Preparation | Setup (outside Risksheet) | Document type, team, scope |
| 2 | Structure Analysis | Default | Item, Function, Requirements |
| 3 | Function Analysis | 1. Identify Failure Modes | + Failure Mode, Failure Effects |
| 4 | Failure Analysis | 2. Initial Risk Ranking | + Severity, Occurrence, Detection, Pre-AP |
| 5 | Risk Analysis | 3. Link Downstream DFMEA | + Downstream Risks (causes link) |
| 6 | Optimization | 4. Define Mitigations, 5. Verify Controls | + Risk Controls, Test Cases |
| 7 | Results Documentation | 6. Final Risk Evaluation, 7. Risk Summary | + Post-mitigation S/O/D, Post-AP |
Multi-Level FMEA Cascade
Unlike ISO 26262’s single HARA analysis at the vehicle level, AIAG-VDA requires Design FMEA (DFMEA) at three hierarchical levels:
TestAuto2 implements this cascade through the causes relationship in its risksheet configurations. A failure mode at the system level can link to multiple downstream failure modes at the subsystem level, which in turn link to component-level root causes. The System DFMEA Report visualizes this hierarchy as a drill-down tree.
Separately, Process FMEA (PFMEA) analyzes manufacturing and assembly processes:
Unlike DFMEA which uses Action Priority, PFMEA in TestAuto2 still uses traditional RPN calculation (S × O × D) because process risks typically involve controllable occurrence rates and measurable detection capabilities.
Why Severity Never Changes Post-Mitigation
A common misconception: “We added a safety control, so severity should decrease.” This is incorrect per AIAG-VDA.
Severity represents the inherent consequence of a failure mode occurring — it describes “what happens IF the failure occurs,” not “how likely it is.” Risk controls reduce occurrence (making failures less likely) and improve detection (catching failures before they cause harm), but they cannot change the physics of what happens when the failure actually occurs.
If a brake cable snap causes vehicle collision (S=10), installing a redundant cable reduces occurrence (now both must snap), but IF both snap, the consequence remains collision (S=10). TestAuto2 enforces this by using the same fmSeverity field value for both pre-mitigation and post-mitigation AP calculations.
SC/CC Special Characteristics
AIAG-VDA integrates with IATF 16949 requirements for Special Characteristics — product or process parameters that can affect safety, regulatory compliance, or critical customer requirements:
- SC (Safety Critical): Directly affects occupant safety or regulatory compliance
- CC (Critical Characteristic): Affects fit/function/durability but not immediate safety
TestAuto2 automatically propagates SC/CC classifications through the traceability chain:
SC characteristics typically require 100% inspection with statistical process control, while CC characteristics may use sampling plans. The Control Plan Risksheet displays SC/CC badges using orange (SC) and red (CC) color coding.
Integration with ISO 26262
TestAuto2 unifies AIAG-VDA FMEA with ISO 26262 functional safety requirements:
| Aspect | ISO 26262 | AIAG-VDA FMEA | TestAuto2 Integration |
|---|
| Risk Metric | ASIL (QM, A-D) | Action Priority (L/M/H) | Parallel fields: asil + premitigationAP |
| Scope | Hazards at vehicle level | Failure modes at all levels | HARA feeds system requirements → SFMEA |
| Mitigation | Safety goals → requirements | Risk controls → test cases | Safety goals become system requirements verified by test cases linked to risk controls |
| Coverage | ISO 26262-8 traceability | FMEA coverage by system element | Requirements Traceability Report + FMEA Coverage Report |
Practical Application in TestAuto2
To apply AIAG-VDA FMEA methodology in your project:
- Structure Analysis: Define system elements using the System Structure Navigator
- Create FMEA Documents: Start at system level with Create System FMEA, cascade to subsystem/component
- Progressive Analysis: Use workflow views to enforce the seven-step process — Define Failure Modes, Assess S/O/D, Calculate Action Priority
- Link Controls: Connect failure modes to Risk Controls and verification test cases
- Track Mitigation: Update occurrence/detection ratings, monitor Post-Mitigation AP
- Generate Reports: Use FMEA Reports to demonstrate risk reduction for management and auditors
The FMEA Reports Dashboard provides executive visibility into DFMEA and PFMEA coverage across your project, while the Risk Control Effectiveness Report validates that mitigation measures actually reduced risk per AIAG-VDA requirements.
