Intermittent Fault
This is a fault that appears only with vibration, temperature change or a particular mechanical position and is invisible in a static measurement. It is the most common reason for devices that work when they reach the service bench but stop in the field. Diagnosis requires reproducing the condition under which the fault occurs in the workshop.
An intermittent fault is mechanical in origin: a loosened terminal, a pin that has backed out inside the housing, strands starting to break under a crimp, a solder joint that expands with heat and loses contact. While the circuit is at rest the contact is adequate; when movement or temperature changes, it breaks.
- Triggering: while the measurement is running, shake the harness by hand, press gently on the connectors, warm the line with a heat gun or apply freezer spray.
- Type of measurement: instead of continuity, measure voltage drop under load and preferably use an instrument that records; momentary spikes are hard to catch by eye.
- Common sources: vibration fatigue, an oxidised connector pin, a loose chassis bolt, a terminal under tensile load.
On vehicle-mounted installations, making the fault repeatable is half the diagnosis. If the fault only appears while the vehicle is moving, review the mechanical stress points along the routing instead of wasting time on static measurements.
Context in which this term is used: Installation, redundancy and field continuity