SPN 637 — Engine Timing Sensor (Crankshaft)
System: Engine
Crankshaft position/speed signal, the main reference for engine speed and timing.
Can I keep running it?
HIGH — limit use, diagnose now
Can cause stalling or no-start.
Likely causes
- Faulty crank sensor
- Wrong air gap or debris
- Damaged flywheel tone ring
- Wiring fault
Checks & fixes (easiest first)
- Inspect sensor and connector
- Check resistance and AC output while cranking
- Scope the crank and cam signals
- Check for SPN 636 together
Common FMIs with SPN 637
- SPN 637 FMI 2Data erratic, intermittent, or incorrect
- SPN 637 FMI 5Current below normal or open circuit
- SPN 637 FMI 8Abnormal frequency, pulse width, or period
- SPN 637 FMI 10Abnormal rate of change
Related codes
FAQ
What does SPN 637 mean?
SPN 637 is Engine Timing Sensor (Crankshaft). Crankshaft position/speed signal, the main reference for engine speed and timing.
Can I keep running with SPN 637?
Can cause stalling or no-start.
What causes SPN 637?
Faulty crank sensor; Wrong air gap or debris; Damaged flywheel tone ring; Wiring fault.