John Deere Engines SPN637FMI5 Fault Code: Crankshaft Position Circuit Has High Resistance
Also called Crank Sensor Circuit Has High Resistance, Crankshaft Position Circuit has High Resistance, Crankshaft Position Sensor Circuit Has High Resistance
Crankshaft Position Circuit Has High Resistance · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 637 FMI 5 means the John Deere ECU has detected high resistance or an open circuit in the crankshaft position sensor circuit. The engine keeps running because the ECU switches to the camshaft position sensor for speed and position, but the fault needs attention soon. Alarm level is listed as Warning.
Medium severity. This is logged as a Warning-level alarm, not a shutdown code. The ECU compensates by using the camshaft position sensor, so the engine can keep running, but a degraded crankshaft position signal should be diagnosed before it worsens or the camshaft sensor also has trouble.
What does John Deere Engines error code SPN637FMI5 mean?
SPN 637 FMI 5 tells you the ECU has found high resistance, or a partial open, somewhere in the wiring or connectors feeding the crankshaft position sensor. This sensor tells the ECU exactly where the crankshaft is and how fast it's turning, which the ECU uses for fuel and timing control.
When the circuit resistance climbs too high, the signal gets weak or unreliable, and the ECU can no longer trust it. Rather than shutting the engine down, the ECU falls back on the camshaft position sensor to keep tracking engine speed and position so the engine keeps running.
This code sets when the ignition is on and the engine is stopped, while the ECU runs its periodic diagnostic check, or during a Harness Diagnostic Mode Test run in Service ADVISOR. It is flagged as a Warning, meaning the system is still operating but running in a backup mode.
What triggers a John Deere Engines SPN637FMI5 code?
The code sets when the ignition is on and the engine is stopped, as the ECU performs its periodic diagnostic check, or during a Harness Diagnostic Mode Test in Service ADVISOR. The ECU detects high resistance or an open circuit in the crankshaft position sensor circuit during that check.
Common causes of SPN637FMI5
- Bad terminals or connector at the crankshaft position sensor, often from corrosion, loose pins, or moisture intrusion
- A bad crankshaft position sensor itself
- A bad harness between the ECU and the crankshaft position sensor, such as chafed, pinched, or corroded wiring
- Bad terminals or connector at the ECU end of the circuit
How to troubleshoot John Deere Engines SPN637FMI5: first checks
- . Inspect the crankshaft position sensor connector and terminals for corrosion, bent pins, or a loose fit before disconnecting anything else
- Visually trace the harness between the ECU and the crankshaft position sensor, looking for chafe points, pinches, or heat damage along its length
- Check the ECU end connector and terminals for the same corrosion or looseness issues found at the sensor end
- Run the Harness Diagnostic Mode Test in Service ADVISOR to let the ECU re-check circuit resistance and confirm whether the fault is still active
- Clean and reseat all connectors in the circuit, then recheck for the code before replacing any parts
How the code clears
No separate clearing step is listed beyond correcting the wiring, connector, or sensor fault. Once the high resistance condition is repaired, the ECU's periodic diagnostic check or a Harness Diagnostic Mode Test run in Service ADVISOR should confirm the circuit is back within range and the active fault should clear on its own.
Frequently asked questions
What does SPN 637 FMI 5 mean on a John Deere engine?
It means the ECU has detected high resistance or an open circuit in the crankshaft position sensor circuit. The engine can keep running because the ECU switches to the camshaft position sensor for speed and position information.
Can I keep operating the machine with this code active?
The alarm level is listed as Warning, and the ECU compensates using the camshaft position sensor, so the engine typically keeps running. Still, it's best to diagnose the wiring or sensor issue soon rather than run indefinitely on a backup signal.
What usually causes SPN 637 FMI 5?
The listed causes are bad terminals or connector at the crankshaft position sensor, a bad crankshaft position sensor, a bad harness between the ECU and the sensor, or bad terminals or connector at the ECU.
How do I start diagnosing this fault?
Start by inspecting the connectors and terminals at both the crankshaft position sensor and the ECU for corrosion or looseness, then trace the harness between them for damage. Running the Harness Diagnostic Mode Test in Service ADVISOR helps confirm the circuit resistance directly.
Does this code mean the crankshaft position sensor is bad?
Not necessarily. A bad sensor is one possible cause, but bad connectors or terminals at either end, or harness damage in between, can produce the same high resistance reading.
Will this code clear itself after a repair?
No separate clearing step is listed. Once the wiring, connector, or sensor problem is fixed, the ECU's own periodic diagnostic check or a Harness Diagnostic Mode Test should confirm the circuit is normal and the active fault should clear.