Introduction
In the previous blog of this series, we introduced Failure Modes and Effects Analysis (FMEA) as a structured way for developers to anticipate failures and improve system reliability. That introduction focused on the fundamentals such as failure modes, effects, causes, severity, occurrence, detection, and risk priority numbers (RPN).
FMEA is not a single, monolithic activity, it takes different forms depending on where it is applied. Developers face various types of FMEA throughout the product lifecycle: Design FMEA (DFMEA), Process FMEA (PFMEA), Software FMEA (SFMEA), and System FMEA. Each type has a distinct purpose.
Today, we will explore each type of FMEA in detail and illustrate scenarios that bring the concepts to life. FMEA is about embedding reliability thinking into your daily work.
Design FMEA (DFMEA)
DFMEA focuses on design elements of both hardware and software, that could fail before the product even reaches manufacturing. The purpose is to identify weaknesses in design and mitigate them early.
For developers, DFMEA usually means looking at software architecture, APIs, and module-level logic. For example:
- A firmware engineer might ask, What if the watchdog timer is not initialized correctly?
- An embedded UI developer might ask, What if the cluster rendering engine runs out of memory?
Developer Roles in DFMEA
- Firmware Developer: Identify low-level software design risks such as buffer overflows, memory leaks, or incorrect driver initialization.
- UI/Feature Developer: Explore failure modes related to user interface, timing issues, or incorrect feature implementation.
- Architect/Lead: Ensure cross-module interactions are safe, validate design assumptions, and define fallback strategies.
- QA Engineer: Suggest test cases that align with identified design failure modes.
Example Scenario
In an automotive cluster, the speedometer relies on CAN data. If the parsing function in the design ignores range check and rate of change check, a corrupted or wrong packet might still be accepted. The effect is a wrong speed displayed, which could be catastrophic. In DFMEA, this risk is identified and mitigated by mandating range check and rate of change check in the design before code implementation.
Process FMEA (PFMEA)
PFMEA focuses on the processes used to build, flash, and test the product. It is less about design and more about how the design is realized. Developers might think this belongs to manufacturing engineers, but there are critical touchpoints where they must be involved.
For instance, consider the firmware flashing process during production. A developer must ensure that the software supports proper error messages and rollback mechanisms if flashing fails. Similarly, automated test scripts written by QA engineers form part of the manufacturing process, and failures in these scripts must be analyzed.
Developer Roles in PFMEA
- Firmware Developer: Ensure reliable flashing routines, error handling, and diagnostic messages are included in the code.
- Tool Developer: Guarantee that automated test and flashing tools are robust with retry mechanisms.
- QA Engineer: Validate that process failures (like incomplete flashing) are detected and logged properly.
- Lead/Architect: Align software deliverables with manufacturing capabilities and ensure maintainability in the process.
Example Scenario
In an industrial controller, if the production process uses a test script that fails to check firmware version compatibility, outdated firmware might be flashed. The effect could be system malfunction at the customer site. PFMEA would identify this risk and require a mandatory version check before flashing.
Software FMEA (SFMEA)
SFMEA is a specialized form of DFMEA focused entirely on software. As systems grow more software-driven, SFMEA has become critical. It digs into failure modes inside code modules, APIs, communication stacks, and algorithm logic.
For developers, this is the most direct type of FMEA. It involves asking questions like:
- What happens if a buffer size is exceeded during CAN data parsing?
- What if a race condition occurs in the multithreaded UI handler?
- What if error codes from a library call are not handled?
Developer Roles in SFMEA
- Firmware Developer: Analyze risks in low-level drivers, interrupt handling, and resource allocation.
- Application Developer: Evaluate API misuse, invalid inputs, and exception handling.
- QA Engineer: Use SFMEA to generate negative test cases and stress test scenarios.
- Architect/Lead: Ensure that coding standards, defensive programming practices, and fail-safe mechanisms are defined.
Example Scenario
In a digital pH meter, the software converts raw sensor voltage into a pH value using a calibration formula. If the calibration coefficients are corrupted (e.g., due to memory error or improper calibration procedure), the algorithm may output an incorrect pH value. Through SFMEA, developers identify this failure mode and implement safeguards such as Range validation (reject values outside 0–14 pH), Redundant calibration data storage and Error flags/alerts to the user.
System FMEA
System FMEA takes a holistic view of how different components such as hardware, software, mechanical parts, and external systems interact. It addresses failures that may not be apparent when looking at individual modules but arise from system-level integration.
Developers often assume system-level failures are outside their scope, but they play a major role. For instance:
- If two ECUs reboot simultaneously due to a shared power glitch, does the software handle recovery gracefully?
- If multiple threads contend for a shared resource across modules, does the system degrade or crash?
- If cloud connectivity drops, does the system enter a safe fallback mode?
Developer Roles in SFMEA
- Firmware Developer: Ensure modules behave gracefully under system-level stresses such as power glitches or bus errors.
- Application Developer: Handle dependencies with other modules or external services.
- QA Engineer: Perform integration testing and simulate real-world stress scenarios.
- Architect/Lead: Model system-level dependencies, define safety-critical paths, and identify single points of failure.
Example Scenario
In a connected vehicle gateway, if cloud connectivity drops during a firmware OTA update, multiple ECUs might be left in inconsistent states. System FMEA would identify this as a failure mode and require a rollback strategy across ECUs to maintain system integrity.
Comparing Types of FMEA and Developer Roles
| Type of FMEA | Focus Area | Developer Roles |
|---|---|---|
| DFMEA | Design-level risks (hardware/software) | Firmware developers check drivers, UI developers analyze features, architects ensure cross-module safety, QA suggests tests |
| PFMEA | Manufacturing/assembly/testing processes | Firmware developers ensure flashing reliability, tool developers build robust scripts, QA validates detection, leads align with process |
| SFMEA | Software module and code-level risks | Firmware developers analyze low-level logic, app developers validate APIs, QA generates negative test cases, architects define standards |
| System FMEA | End-to-end system integration and dependencies | Firmware developers handle glitches, app developers manage module dependencies, QA simulates stress, architects identify system weak points |
Conclusion
FMEA comes in many forms such as DFMEA, PFMEA, SFMEA, and System FMEA and each has unique value. For developers, understanding these types is very important.
DFMEA helps you catch risks in design before coding starts. PFMEA ensures that manufacturing and testing processes don’t introduce new failures. SFMEA pushes you to analyze software logic in depth, making your code safer. And System FMEA ensures the overall system behaves predictably under stress.
