Intermittent Fault Diagnosis
Canonical Definition
Intermittent fault diagnosis reproduces and captures a failure whose presence depends on changing operating conditions, using state logging, non-destructive stress tests, synchronized measurements, and evidence preserved at the moment the fault occurs.
Build A State Matrix
| Variable | Examples |
|---|---|
| time | immediate, after minutes, after hours, after sleep |
| temperature | cold start, cabin heat, amplifier heat, sunlight |
| motion and vibration | door movement, seat travel, bumps, engine vibration |
| electrical load | bass hit, headlights, HVAC, charging, stop-start |
| source and control | Bluetooth, USB, radio, call, prompt, preset, fader |
| vehicle state | key cycle, accessory, running, reverse, sleep, wake |
Capture Before Disturbance
Do not move the harness, cycle power, or cool the amplifier before recording:
- device-terminal voltage and ground-side drop
- remote, enable, mute, and protection state
- signal before and after the suspected boundary
- temperature and time to failure
- source, preset, volume, and vehicle state
Useful Capture Tools
- DMM min/max for slower supply interruptions
- oscilloscope single-shot or segmented memory for brief dropouts
- audio recorder or analyzer for signal loss and noise
- telemetry or data logger for temperature, voltage, current, and control state
- camera focused on fault indicators and the operating condition
Controlled Stress Tests
Stress one zone at a time. Use gentle connector pressure, defined harness movement, controlled temperature, or repeatable vibration within the component and vehicle limits. A test that creates a new open, short, cracked joint, or overheated part is not diagnostic evidence.
Verification Must Match The Failure
If the original failure took 40 minutes of heat and road vibration, a five-minute parked test is not enough. Repeat the relevant duration, cycles, temperature, movement, source, and load, then check adjacent conditions for regressions.
Road-Test Safety
Use a second person or automated logging. Do not manipulate high-current, restraint, or network wiring while the vehicle is moving.