Glossary · Maintenance and diagnostics
Failure mode
Also known as: Mode of failure
German: Ausfallart
In dependability engineering, a failure mode is the manner in which a failure occurs, for example an item that does not start, stops unexpectedly, drifts out of tolerance or fails in an open or closed state.
- Maintenance
In one sentence
A failure mode is the manner in which an item fails, such as failing open, failing closed, drifting or stopping unexpectedly.
Example
For a solenoid valve, the FMEA lists the failure modes "does not open", "does not close" and "leaks internally".
How it applies
- Engineering: Listing the failure modes of each component is the starting point of an Failure Modes and Effects Analysis (FMEA) and of the safe/dangerous failure split used in functional safety.
- Design: Knowing the failure modes lets designers choose components and circuits so that likely modes lead to a safe state, see Fail-safe behavior.
- Diagnostics: Diagnostic functions are designed to detect specific failure modes; the share they detect is expressed as Diagnostic coverage (DC).
- Documentation: Troubleshooting sections can be organized by observable failure mode ("motor does not start"), which matches how readers experience a problem.
Failure mode vs. failure cause
A failure mode is the observable way something fails. A Failure cause is the reason behind it. One failure mode can have several causes, and one cause can produce several failure modes.