FMI 8 — Abnormal frequency, pulse width or period
The signal is there but the timing of it is wrong — wrong pulse rate, wrong duty cycle, wrong spacing.
Common causes
- Damaged tone/reluctor wheel or debris on it
- Incorrect sensor air gap
- Failing speed or position sensor
- Shielding or routing problem picking up noise
What to test, in order
- Scope the signal and compare waveform, amplitude and spacing to a known-good
- Inspect the tone ring for missing or damaged teeth and metal debris
- Set the sensor air gap to spec
- Verify the shield ground is intact and the harness is routed away from ignition/charging noise
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