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Overview

The FMEA Severity scale ranges from 1 (No Effect) to 10 (Safety-Critical / Regulatory Non-Compliance), with each level representing a distinct operational or customer impact category. Severity is one of three dimensions in the Risk Priority Number (RPN) calculation, alongside Occurrence and Detection: 
RPN = Severity × Occurrence × Detection
Unlike Occurrence and Detection, severity does not change after mitigation controls are implemented. The fundamental nature of the failure remains; only the likelihood and detectability of the failure are reduced by controls.

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Severity Levels Reference

LevelCategoryOperational ImpactCustomer DetectionAutomotive ContextASIL MappingColor
10Safety-Critical (Unwarned)Loss of vehicle control or inability to fulfill safety function. Regulatory non-compliance likely (ASIL D).Customer immediately aware; failure is unavoidable during operation.Brake system failure, steering loss, uncontrolled accelerationASIL DDark Red
9Safety-Critical (Warned)Loss of vehicle control or safety function with driver warning available. May result in ASIL C or D classification depending on controllability.Customer immediately aware if warning heeded; failure avoidable if warning is recognized.Engine shutdown with warning, reduced power mode with indicatorASIL C/DFirebrick
8Major Disruption (Inoperable)Complete loss of non-safety primary function. Vehicle is still operable but severely degraded. Up to 100% of product may have to be scrapped in manufacturing.Customer frustrated; vehicle must be serviced immediately.Complete loss of engine power, transmission lock, fuel pump failureHigh Manufacturing RiskCrimson
7Major Disruption (Performance)Significant reduction in non-safety function performance or comfort. Vehicle remains operable with noticeably reduced capability.Customer aware of reduced performance; vehicle operates but is inconvenient.Reduced engine power, degraded transmission shift quality, poor fuel economyOperational DegradationOrange-Red
6Moderate (Comfort/Convenience Inoperable)Complete loss of comfort or convenience feature. Primary driving functions remain fully operational.Customer dissatisfied; comfort feature must be repaired but does not affect safety.Climate control failure, window/mirror failure, infotainment system failureWarranty Cost ImpactDark Orange
5Moderate (Reduced Convenience)Reduced performance of comfort or convenience feature, but feature remains partially operational.Customer notices reduced functionality; minor dissatisfaction.Climate control reduced capacity, slow window operation, degraded audio qualityModerate Warranty CostLight Pink
4Minor (Fit and Finish, 50-75% Detection)Cosmetic or fit-and-finish defect noticeable by roughly 50-75% of customers who inspect the defect. Examples: squeak, rattle, paint run, panel gap.Approximately 50-75% of customers will detect the defect during ownership.Squeak/rattle in door, loose trim panel, slight paint overspray, misaligned body panelLow Warranty CostYellow
3Minor (Fit and Finish, 25-50% Detection)Cosmetic defect noticeable by roughly 25-50% of customers. May require close inspection to detect.Approximately 25-50% of customers will detect the defect; discriminating customers will notice.Slight squeak audible only in quiet cabin, barely visible paint blemish, minor panel gapVery Low Warranty CostPale Yellow
2Negligible (Fit and Finish, <25% Detection)Cosmetic defect detected by fewer than 25% of customers; only discriminating customers or detailed inspections will find it.Fewer than 25% of customers will detect; most customers will not notice.Nearly imperceptible color variation, minimal trim misalignment, barely audible squeakNegligible Warranty CostSilver
1No EffectFailure has no discernible impact on vehicle operation, customer satisfaction, or regulatory compliance.Customer completely unaware of failure.Spare part unused, redundant sensor, pre-staged component never activatedNo ImpactBright Green

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Severity Classification Guidance

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Safety-Critical Failures (Levels 10, 9)

Level 10 applies when:
  • Failure results in loss of vehicle control, inability to stop, or loss of critical safety function
  • No driver warning or mitigation available; failure is unavoidable
  • ISO 26262 ASIL D classification likely
  • Regulatory non-compliance or recall risk is high
Level 9 applies when:
  • Failure results in loss of safety function WITH driver warning or controllability mitigation
  • Warning or indication is available, making failure avoidable if properly heeded
  • ISO 26262 ASIL C or D classification possible
  • Controllability assessment will determine final ASIL rating
Example decision tree: Failure: “Loss of engine power” └─ Is there a warning light? ├─ NO → Severity 10 (unwarned, uncontrollable) └─ YES → Is the driver able to safely coast to a stop? ├─ NO → Severity 10 (warning exists but failure is uncontrollable) └─ YES → Severity 9 (warned, controllable)

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Operational Impact Failures (Levels 8, 7)

Level 8 (Complete inoperability) applies when:
  • Primary vehicle function becomes completely inoperable
  • Vehicle is unsafe to drive or cannot be driven at all
  • Potential for widespread manufacturing recalls or high warranty costs
  • Example: Complete transmission failure, total brake loss (non-safety scenario), engine stall
Level 7 (Degraded performance) applies when:
  • Primary vehicle function is significantly reduced but still operational
  • Vehicle can be driven but with noticeably poor performance
  • Example: Reduced engine power output, sluggish transmission response, poor fuel economy

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Comfort/Convenience Failures (Levels 6, 5)

Level 6 (Complete loss) applies when:
  • Comfort or convenience feature becomes completely inoperable
  • Primary driving functions are unaffected
  • Example: Climate control completely dead, power windows non-functional, infotainment system blank
Level 5 (Reduced function) applies when:
  • Comfort or convenience feature operates but at reduced performance
  • Some functionality remains; partial operation is possible
  • Example: Climate control blows only cold air, window operates slowly, audio cuts in and out
Do NOT use levels 5-6 for failures affecting primary vehicle functions (steering, braking, acceleration). Those failures belong in levels 7-10 depending on severity and controllability.

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Fit-and-Finish / Cosmetic Failures (Levels 4, 3, 2, 1)

These levels depend on customer detection probability — the percentage of customers who will notice the defect during ownership:
LevelDetection RateDefinitionExamples
4>75% (High)Most customers will notice this defectLoud squeak in door, visible paint run, obvious panel gap, loose trim that rattles
3~50% (Medium)About half of customers will noticeSubtle squeak only audible in quiet cabin, barely visible paint blemish, slight panel misalignment
2<25% (Low)Only discriminating or very attentive customers noticeNearly imperceptible color variation, minimal trim gap, almost inaudible squeak
1Not detectedNo customer will ever detect; no discernible effectSpare part never used, redundant component, pre-staged failsafe never activated
Detection rate thresholds:
  • >75%: Any defect that is obvious during casual use or inspection (e.g., the customer notices without deliberate searching)
  • ~50%: Defects that are noticeable if the customer pays attention or inspects carefully; some customers will miss it
  • <25%: Defects that require careful inspection or detailed comparison; only perfectionist or discriminating customers will find it
  • 1 = No effect: The failure is undetectable or irrelevant (e.g., a redundant component fails but a backup takes over)
In automotive NVH (Noise, Vibration, Harshness) analysis, use these guidelines:
  • Level 4: Loud, obviously present in normal driving conditions
  • Level 3: Noticeable in quiet conditions or at specific speeds; audible but not constant
  • Level 2: Barely audible; requires quiet cabin and specific circumstances to hear
  • Level 1: Inaudible even under test conditions

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Severity and ASIL Relationship

Severity is one of three inputs to the ISO 26262 ASIL determination matrix (combined with Exposure and Controllability). However, FMEA severity and HARA severity serve different purposes:
  • HARA Severity (S0-S3): Describes potential harm to people, used in hazard analysis for ASIL classification
  • FMEA Severity (1-10): Describes impact of a failure mode on vehicle operation and customer satisfaction, used for RPN prioritization
A single HARA hazard may spawn multiple FMEA failure modes with varying FMEA severity ratings, all contributing to the same ASIL classification.
Severity level 10 explicitly includes the note “Regulatory non-compliance likely (ASIL D)” to flag failures that require the highest safety integrity level per ISO 26262. When you assign severity 10, verify that a corresponding safety goal exists in the HARA analysis.

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RPN Calculation and Thresholds

Severity is multiplied with Occurrence and Detection to compute the Risk Priority Number (RPN): 
RPN = Severity (1-10) × Occurrence (0-10) × Detection (0-10)
Maximum RPN = 10 × 10 × 10 = 1,000
Common RPN action thresholds (may be adjusted per project policy):
  • RPN ≥ 300: Require corrective action (either reduce Occurrence or improve Detection)
  • RPN 100-300: Recommend corrective action or enhanced monitoring
  • RPN < 100: Accept risk; routine controls may be sufficient
Impact of Severity on RPN:
  • A failure with Severity 10 and Occurrence 2, Detection 5 yields RPN = 100 (requires action)
  • A failure with Severity 1 and Occurrence 10, Detection 10 yields RPN = 100 (accept risk)
This demonstrates why severity and occurrence must both be considered for risk prioritization.

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Configuration in TestAuto2

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Enumeration Definition

The FMEA Severity enumeration is defined in the Polarion project configuration: 
<enum id="fmea-severity">
  <name>FMEA Severity</name>
  <enum-value id="1" sortOrder="10" iconURL="...icon-trivial...">
    <name>1 - No Effect</name>
  </enum-value>
  <enum-value id="2" sortOrder="9" iconURL="...icon-low...">
    <name>2 - Negligible (NVH <25%)</name>
  </enum-value>
  <!-- ... levels 3-10 ... -->
  <enum-value id="10" sortOrder="1" iconURL="...icon-highest...">
    <name>10 - Safety-Critical / Regulatory Non-Compliance (ASIL D)</name>
  </enum-value>
</enum>
Sort order note: Levels are sorted from 10 (highest risk, sort order 1) to 1 (lowest risk, sort order 10), ensuring high-severity failure modes appear at the top of prioritized FMEA views.

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Risksheet Integration

Severity is displayed as an editable dropdown column in the FMEA risksheet:
  • Column type: Enumeration picker (dropdown)
  • Default value: Unanalyzed (0) or 5 (Moderate)
  • Cell styling: Custom cell decorator renders severity as a large colored badge with text label
  • Row header coloring: Row headers often inherit color from the post-mitigation Action Priority, NOT severity
  • Filtering: High-severity failure modes can be filtered to prioritize critical risk analysis

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Formulas and Dependencies

Severity feeds into several automated formulas:
  1. Action Priority (AP) Calculation: AP = f(Severity, Occurrence, Detection)
    • Severity ≥ 8 and Occurrence ≥ 8 typically → High priority
    • Severity ≥ 8 or Occurrence ≥ 8 typically → Medium priority
    • Otherwise → Low priority
  2. RPN Calculation: RPN = Severity × Occurrence × Detection
  3. Risk Flag: Severity 9-10 may automatically flag failure mode for escalation or safety review

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Custom Field Binding

The severity field is bound to the Failure Mode work item type:
PropertyValue
Work Item TypefailureMode
Field IDfailureModeSeverity
Display NameSeverity (1-10)
TypeEnumeration
RequiredYes (in FMEA risksheet)
Multi-SelectNo