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SPN 637 FMI 10

Engine Timing Sensor (Crankshaft) — Abnormal rate of change.
The value is changing faster than is physically believable.

What the SPN covers: Crankshaft position/speed signal, the main reference for engine speed and timing. More on SPN 637.

What FMI 10 usually points to: Intermittent wiring, a sensor glitch, or a sudden real event such as a burst hose. More on FMI 10.

Severity

HIGH — limit use, diagnose now

Can cause stalling or no-start.

Likely causes

  1. Faulty crank sensor
  2. Wrong air gap or debris
  3. Damaged flywheel tone ring
  4. Wiring fault

Checks & fixes (easiest first)

  1. Inspect sensor and connector
  2. Check resistance and AC output while cranking
  3. Scope the crank and cam signals
  4. Check for SPN 636 together

FAQ

What does SPN 637 FMI 10 mean?

Engine Timing Sensor (Crankshaft) — abnormal rate of change. The value is changing faster than is physically believable.

Is SPN 637 FMI 10 serious?

Can cause stalling or no-start.

What should I check first for SPN 637 FMI 10?

Inspect sensor and connector; Check resistance and AC output while cranking; Scope the crank and cam signals.