John Deere Engines SPN636FMI6 Fault Code: Camshaft Position Circuit Has Low Resistance
Also called Camshaft Position Circuit has Low Resistance
Camshaft Position Circuit Has Low Resistance · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 636 FMI 6 means the John Deere ECU has detected low resistance or a short circuit in the camshaft position sensor circuit. This is set as a Warning alarm level. The ECU compensates by using the crankshaft position sensor for engine speed and position, so the engine typically keeps running.
Medium severity. The alarm level is listed as Warning, and the ECU has a built-in fallback that uses the crankshaft position sensor to keep the engine running. Because of that fallback, this is not usually an immediate stop-the-engine situation, but the camshaft signal loss should still be diagnosed promptly since it affects redundancy and can point to a developing wiring or sensor failure.
What does John Deere Engines error code SPN636FMI6 mean?
SPN 636 FMI 6 is a John Deere engine fault code that fires when the ECU detects low resistance, a short circuit, or an open circuit in the wiring or sensor that reports camshaft position. The camshaft position sensor helps the ECU know exactly where the camshaft is in its rotation, which matters for fuel injection timing and, on many engines, cylinder identification during startup.
When this circuit reads abnormally low resistance, the ECU can no longer trust the camshaft signal. Rather than shutting the engine down, the ECU falls back to using the crankshaft position sensor alone to determine engine speed and position, and keeps trying to maintain proper operating conditions.
This code can be triggered actively while the engine is running or stopped with the ignition on, and it also shows up during the ECU's own periodic diagnostic checks and during a Harness Diagnostic Mode Test run in Service ADVISOR.
What triggers a John Deere Engines SPN636FMI6 code?
The code is displayed when the ignition is on and the engine is stopped and the fault is active, or as part of the ECU's periodic diagnostic check, or during a Harness Diagnostic Mode Test in Service ADVISOR. The underlying condition is low resistance, a short circuit, or an open circuit detected in the camshaft position sensor circuit during these checks.
Common causes of SPN636FMI6
- Bad terminals or connector at the camshaft position sensor, including corrosion, looseness, or damaged pins
- A bad camshaft position sensor itself
- A bad harness or short in the wiring between the ECU and the camshaft position sensor
- Bad terminals or connector at the ECU end of the circuit
How to troubleshoot John Deere Engines SPN636FMI6: first checks
- Inspect the camshaft position sensor connector for corrosion, moisture, bent or pushed-back pins, and a full, secure seat
- Trace the harness between the ECU and the camshaft position sensor for chafing, pinch points, or damaged insulation that could cause a short or low-resistance path
- Check the ECU-side connector and terminals for the same corrosion, looseness, or pin damage found at the sensor end
- Run the Harness Diagnostic Mode Test in Service ADVISOR to help isolate whether the fault is in the sensor, the harness, or the ECU connector
- Inspect or test the camshaft position sensor itself if the wiring and connectors check out clean
How the code clears
No separate clearing step or reset procedure is listed for this code. Once the underlying wiring, connector, or sensor problem is repaired, the ECU's periodic diagnostic check and the Harness Diagnostic Mode Test can be used to confirm the fault no longer sets.
Frequently asked questions
What does SPN 636 FMI 6 mean on a John Deere engine?
It means the ECU has detected low resistance, or in some cases a short or open circuit, in the camshaft position sensor circuit. The alarm level is a Warning, and the ECU switches to using the crankshaft position sensor for engine speed and position while the fault is active.
Can I keep running the equipment with this code active?
The ECU is designed to keep the engine operating using the crankshaft position sensor as a backup, and the alarm level is listed as Warning rather than a shutdown-level fault. Even so, it should be diagnosed and repaired promptly since you are running without camshaft position redundancy.
What usually causes SPN 636 FMI 6?
The listed causes are bad terminals or connector at the camshaft position sensor, a bad camshaft position sensor, a bad harness or short in the wiring between the ECU and the sensor, and bad terminals or connector at the ECU.
How do I diagnose this code in the field?
Start by inspecting the connectors and terminals at both the camshaft position sensor and the ECU for corrosion or damage, then check the harness between them for shorts or chafing. Running the Harness Diagnostic Mode Test in Service ADVISOR helps pinpoint whether the issue is in the sensor, harness, or connectors.
Does this code trigger a specific engine speed or temperature threshold?
No specific rpm, voltage, or temperature threshold is listed for this code. It is set based on the ECU detecting low resistance or a short/open circuit condition during its periodic diagnostic check or the Harness Diagnostic Mode Test, not a numeric operating threshold.
Is there a reset procedure after fixing the wiring or sensor?
No separate reset procedure is listed. Repairing the connector, harness, or sensor issue and then confirming through the ECU's normal diagnostic check or a Harness Diagnostic Mode Test run is the way to verify the fault has cleared.