To do a PFMEA, start from the process flow diagram and work one process step at a time. For each step, list its function and requirements, then the ways it can fail, the effect on the customer, and the cause. Rate severity, occurrence and detection on 1–10 scales, prioritise with Action Priority (or RPN if your customer still uses it), and assign actions that lower occurrence or improve detection. The AIAG & VDA FMEA Handbook organises this into seven steps, from planning to documenting results. The steps below follow that order.
A process FMEA finds the ways a manufacturing or assembly process could produce a bad part, before it does. It is one of the automotive core tools, and it connects the process flow diagram to the control plan. The quality core tools guide, the pillar for this cluster, shows how they fit, and PFMEA vs DFMEA covers the design-side version.
The ratings scales and the Action Priority table belong to the AIAG & VDA FMEA Handbook and to customer manuals. Use the edition your customer requires and do not invent your own scales without agreement.
The most common confusion is between the two control columns. A prevention control acts on the cause before a part is made: a poka-yoke that stops a part loading the wrong way, a validated program, a tool-life counter. A detection control finds the failure mode or cause after it happens: a gauge, a vision check, an inspection. Ratings follow: prevention lowers occurrence, detection lowers the detection rating.
Detection ratings depend on whether the measurement can be trusted. A gauge with poor repeatability does not earn a strong detection rating, so check it with the gauge R&R calculator. Occurrence ratings are easier to defend with data: process capability from the process capability calculator or scrap history.
Keep sessions short and focused on a few process steps at a time, and have the facilitator fill in the worksheet live on a shared screen so everyone sees the wording. Agree on the rating scales at the start and keep them visible; most arguments in a PFMEA are about ratings, and pointing back to the agreed criteria settles them faster. Record assumptions, such as which controls are already in place, so later reviewers understand why a rating was given.
Use real data wherever it exists. Scrap and rework history, customer complaints, warranty returns and capability studies are better evidence for occurrence than opinion. When there is no data for a new process, rate conservatively and plan to revisit the rating after the first production runs. End each session by reading back the actions, owners and dates, and record them in the PFMEA worksheet before anyone leaves.
Example: One PFMEA row for a fictional drilling step, rated before and after action
Result: Example result: the locating pin lowers occurrence from 6 to 2 and the RPN from 294 to 98, while severity stays 7 because the effect has not changed. Look up the Action Priority before and after in the handbook table your customer uses. All ratings are example values set by the fictional team.
It depends on the number of steps and the team’s preparation. Plan several short sessions rather than one long one, and come with the flow diagram and failure history ready.
A DFMEA looks at how the design could fail to meet its function. A PFMEA looks at how the process could fail to make the design. [PFMEA vs DFMEA](/blog/pfmea-vs-dfmea) compares them.
Some customers still ask for it. The 2019 AIAG & VDA handbook replaced it with Action Priority, which considers severity first. Follow your customer’s requirement.
In the AIAG & VDA handbook: planning and preparation, structure analysis, function analysis, failure analysis, risk analysis, optimisation, and results documentation.
Usually manufacturing or process engineering, with quality as a reviewer. It should be under document control and kept in step with the control plan.
New templates, charts and calculators for quality and manufacturing engineers, when they ship.
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