Safety critical dimension OOS, detectable at assembly
8
Product inoperable, 100% scrap
Part cannot be reworked, total loss
7
Product operable but degraded, customer dissatisfied
Performance below spec, customer complaint
6
Product operable, comfort/convenience affected
Cosmetic defect, minor fit issue
5
50% of product may need rework
Significant rework required
4
Product requires sorting/rework
Sorting operation needed
3
Minor rework at station
In-station repair possible
2
Slight inconvenience
Minor adjustment
1
No effect
No discernible impact
Occurrence (O) - Likelihood of Cause
Rating
Failure Rate
Cpk Equivalent
MNMUK Examples
10
Very high: ≥100/1000
<0.33
New process, no controls
9
High: 50/1000
≥0.33
Known problem process
8
High: 20/1000
≥0.51
Similar process had failures
7
Moderately high: 10/1000
≥0.67
Occasional failures observed
6
Moderate: 2/1000
≥0.83
Infrequent failures
5
Moderately low: 0.5/1000
≥1.00
Controlled process, some failures
4
Low: 0.1/1000
≥1.17
Well-controlled process
3
Very low: 0.01/1000
≥1.33
Capable and controlled
2
Remote: 0.001/1000
≥1.50
Proven design and controls
1
Nearly impossible: ≤0.001/1000
≥1.67
Failure eliminated by design
Detection (D) - Ability to Detect Before Customer
Rating
Detection Capability
MNMUK Examples
10
No detection possible
No inspection, no opportunity to detect
9
Unlikely to detect
Random sampling only, infrequent
8
Low: Visual inspection by operator
100% visual check, variable attention
7
Very low: Double visual inspection
Two operators check
6
Low: Charting/SPC
Control charts, trend monitoring
5
Moderate: Attribute gaging
Go/No-go gaging
4
Moderately high: Variable gaging
Measurement with limit checking
3
High: Automated in-process test
Automatic measurement, alarm
2
Very high: Error-proofing
Poka-yoke prevents defect production
1
Almost certain: Error-proofing prevents cause
Design makes failure impossible
Action Priority (AIAG-VDA Approach)
Instead of or in addition to RPN, use Action Priority:
Priority
Criteria
Action Required
HIGH
S=9-10 (any O, D) OR S=7-8 with O≥4 AND D≥4
Immediate action required
MEDIUM
S=5-8 with O≥4 OR D≥4
Action recommended
LOW
All others
Monitor and document
RPN Thresholds (MNMUK Standard)
RPN Range
Priority
Required Action
≥120
Critical
Immediate countermeasure, cannot ship without action
80-119
High
Countermeasure required before PPAP
40-79
Medium
Countermeasure recommended
<40
Low
Monitor, no immediate action
Note: Any Severity ≥8 requires action regardless of RPN.
Countermeasure Hierarchy
When addressing failure modes, apply controls in this priority order:
Eliminate - Design out the failure mode entirely
Substitute - Replace with less hazardous process/material
Engineer - Install physical safeguards, poka-yoke
Admin - Procedures, training, work instructions
Detect - Inspection, testing, monitoring
Special Characteristics
Critical Characteristics (CC)
Safety or regulatory impact
Marked with shield symbol or (CC)
Requires enhanced controls
Mandatory documentation
Significant Characteristics (SC)
Fit, function, or durability impact
Marked with diamond or (SC)
Requires appropriate controls
SPC typically required
Output Format Requirements
CRITICAL: Every PFMEA response MUST be complete. Never truncate or cut off mid-entry. Every failure mode listed MUST have:
All causes fully documented
S/O/D ratings for EVERY cause row
RPN calculated for EVERY row
Current controls listed
Recommended actions specified
After-action ratings included
If the full PFMEA would be very long, reduce the NUMBER of failure modes covered, but each one included MUST be 100% complete. Do not start a failure mode entry you cannot finish.
Output Format
When generating PFMEA content:
# PFMEA: [Part/Process Name]
**Part Number**: [P/N]
**Process**: [Description]
**FMEA Number**: PFMEA-[DEPT]-[SEQ]
**Revision**: [Rev] | **Date**: [YYYY-MM-DD]
**Team**: [Names/Roles]
## Process Step: [Step Name]
### Failure Mode 1: [Description]
**Function**: [What the step should do]
**Effect**: [What happens if it fails]
**Cause**: [Why it would fail]
| S | O | D | RPN | AP |
|---|---|---|-----|-----|
| X | X | X | XXX | H/M/L |
**Current Controls**:
- Prevention: [Current prevention measures]
- Detection: [Current detection measures]
**Recommended Actions**:
- [ ] [Action description] - Owner: [Name] - Due: [Date]
**After Action**:
| S | O | D | RPN | AP |
|---|---|---|-----|-----|
| X | X | X | XXX | H/M/L |
Department-Specific Guidance
Machine Shop
Common failure modes: Dimensional OOS, surface finish, tool wear
Focus on: Fixturing, program parameters, tool life management
Key controls: First piece inspection, SPC, gage R&R
Damper Assembly
Common failure modes: Leak, incorrect torque, missing component
Focus on: Seal integrity, fastener torque, component presence