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SPN 636 FMI 2

Engine Position Sensor (Camshaft) — Data erratic, intermittent, or incorrect.
The signal jumps around, drops in and out, or disagrees with other information the controller has.

What the SPN covers: Camshaft position signal used for injection timing and cylinder identification. More on SPN 636.

What FMI 2 usually points to: Loose or corroded connectors, chafed wiring, a failing sensor, or two redundant sensors that do not agree. More on FMI 2.

Severity

HIGH — limit use, diagnose now

May cause hard starting, rough running or no-start.

Likely causes

  1. Faulty cam sensor
  2. Wrong air gap or debris on the sensor
  3. Damaged tone ring
  4. Wiring fault

Checks & fixes (easiest first)

  1. Inspect the sensor tip for metal debris
  2. Check resistance and wiring
  3. Compare cam and crank signals with a scope
  4. Check for SPN 637 together

FAQ

What does SPN 636 FMI 2 mean?

Engine Position Sensor (Camshaft) — data erratic, intermittent, or incorrect. The signal jumps around, drops in and out, or disagrees with other information the controller has.

Is SPN 636 FMI 2 serious?

May cause hard starting, rough running or no-start.

What should I check first for SPN 636 FMI 2?

Inspect the sensor tip for metal debris; Check resistance and wiring; Compare cam and crank signals with a scope.