What is FMEA Severity rating?

FMEA Severity (S) is a numerical rating from 1 to 10 that evaluates the seriousness of a potential failure mode's effect. A rating of 1 indicates no discernible effect, while 10 indicates a hazardous effect affecting safety. Ratings of 9 or 10 require immediate priority attention regardless of other factors, per AIAG VDA Handbook standards.

How is RPN calculated in FMEA?

Risk Priority Number (RPN) is calculated by multiplying Severity (S) x Occurrence (O) x Detection (D), yielding a value from 1 to 1,000. The AIAG VDA 4th Edition (2019) recommends using Action Priority (AP) instead of RPN, because AP better prioritizes risk by weighting Severity and Occurrence over Detection.

What is the difference between AIAG and VDA FMEA ratings?

The AIAG VDA FMEA Handbook (4th Edition, 2019) is a harmonized standard replacing the separate AIAG FMEA 4th Edition and VDA Volume 4. Key changes include: Action Priority (AP) tables replacing traditional RPN thresholds, updated harmonized SOD criteria, and a new 7-step FMEA methodology. All tables on fmearatings.com reflect the current AIAG VDA standard.

What are the standard FMEA Severity, Occurrence, and Detection (SOD) ratings?

FMEA ratings use a scale from 1 to 10. Severity measures failure impact (1 = no effect, 10 = safety risk), Occurrence ranks failure probability, and Detection assesses how likely controls will find the failure before reaching the customer.

How do I use the FMEA Severity Table 1-10 according to AIAG & VDA standards?

The AIAG VDA FMEA Handbook provides updated criteria for the 1-10 scale. A rating of 9 or 10 always indicates a potential safety or regulatory non-compliance issue. The focus has shifted from calculating RPN to understanding the functional impact of each failure mode.

What is the difference between RPN and Action Priority (AP) in FMEA?

RPN is calculated by multiplying Severity x Occurrence x Detection. The new Action Priority (AP) system uses a logic-based table to categorize risk as High, Medium, or Low. AP is preferred over RPN because it prioritizes the combined impact of severity and occurrence rather than just the product of three numbers.

Where can I find a PFMEA and DFMEA Occurrence Table?

Comprehensive PFMEA and DFMEA occurrence tables are available on fmearatings.com. These tables help assign a ranking from 1 (nearly impossible) to 10 (persistent failure) based on historical data, preventive controls, and predicted failure rates.

Why is a Detection ranking of 10 critical in a risk assessment?

A Detection ranking of 10 means there is no control in place to detect the failure mode. Even if occurrence is low, a detection ranking of 10 often triggers an immediate need for improved inspection methods or automated sensors to protect the end-user.

IATF 16949 FMEA Requirements

Complying with Automotive QMS Risk Analysis Standards

FMEA as a Core Pillar of IATF 16949

IATF 16949:2016 is the global Quality Management System standard for the automotive industry. A central component of IATF 16949 is its focus on risk-based thinking and defect prevention.

Rather than relying solely on sorting out defective products at the end of the line, IATF 16949 requires organizations to anticipate potential failures and build preventive controls. The primary tool used to implement and document this risk analysis is the **Failure Mode and Effects Analysis (FMEA)**.

Key IATF 16949 Clauses Demanding FMEA

FMEA requirements are woven into several sections of the IATF 16949 standard, most notably during the design and development phase:

Clause 8.3.5.1: Design and Development Outputs – Supplemental

This clause requires that product design outputs include a Design FMEA (DFMEA). It also demands that the design review process assesses the DFMEA to verify design robustness.

Clause 8.3.5.2: Manufacturing Process Design Output

This clause dictates that manufacturing process design outputs must include a Process FMEA (PFMEA). The PFMEA evaluates process parameters, tooling, machinery, and potential operator errors to eliminate defects at the station of origin.

FMEA as a "Living Document"

A major point of audit non-compliance is treating the FMEA as static paperwork created solely for PPAP approval. IATF 16949 explicitly expects FMEAs to be active, living documents.

When must you update your FMEA?

Design or Process Changes: Any modification to the part design, raw materials, tooling, production layout, or machinery triggers a review and update of the corresponding FMEA.
Customer Claims / Quality Failures: If a defect escapes your plant and reaches the customer (claims, 8D reports, warranty claims), you must update the FMEA. You must verify if the failure mode and cause were originally identified, recalculate occurrence/detection ratings, and implement corrective actions.
Continuous Improvement: Reviewing FMEAs periodically to lower occurrence ratings based on historical stability data (e.g., Cpk values) and updating controls.

Linking PFMEA to the Control Plan

IATF 16949 audit guidelines (and the AIAG VDA Handbook) enforce a strict connection between the **Process Flow Diagram (PFD)**, **PFMEA**, and the **Control Plan (CP)**.

Process Step Alignment: Every step numbered in the Process Flow Diagram must match the step number and description in the PFMEA and Control Plan.
Special Characteristics: Any characteristic designated as a Special Characteristic (safety, regulatory, key fit/function) in the DFMEA or PFMEA must be marked on the Control Plan.
Risk Controls: For high-priority failure modes (High/Medium Action Priority), the controls listed under "Current Process Controls" in the PFMEA must align exactly with the inspection methods, sample sizes, and reaction plans detailed in the Control Plan.