John Deere Engines SPN636FMI2 Fault Code: Camshaft Position Signal Invalid
Also called Cam Position Input Noise, Pump Position Sensor Input Noise
Camshaft Position Signal Invalid · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN636FMI2 means the ECU is seeing excessive electrical noise, extra pulses, on the camshaft or high-pressure pump position sensor signal. The engine can hesitate, stall, or need prolonged cranking to restart, and if a crankshaft position code sets at the same time, the engine won't restart until one of the two codes is fixed.
High severity. The engine may hesitate or die when the code sets, though it will normally restart on its own using the crankshaft sensor input alone. If a crank position code sets alongside SPN636FMI2, the engine will not start or will stall and stay stalled until one of the two codes is repaired. Because of the stall and hard-restart risk, this should be diagnosed promptly rather than run for extended periods.
What does John Deere Engines error code SPN636FMI2 mean?
SPN636FMI2 points to the camshaft position sensor, also described in some John Deere documentation as the pump position sensor located in the high-pressure fuel pump. This is an inductive pickup that reads notches on a timing wheel, either the camshaft gear or the pump timing wheel depending on the engine, to tell the ECU exactly where cylinder number 1 is in its cycle.
The ECU combines this cam/pump position signal with the crankshaft position signal to calculate precise piston position, correct start of injection timing, and how much fuel to inject at each cylinder. When the ECU detects extra, unexpected pulses on this signal, meaning electrical noise rather than a clean, real signal, it sets FMI 2 (invalid or noisy data) rather than a missing-signal fault.
Because the ECU can still run off the crankshaft sensor alone in this condition, the engine typically keeps running or restarts, but timing precision and startup reliability suffer. If the crankshaft sensor also has a code, the ECU has no reliable position reference left, and the engine will not run.
Common causes of SPN636FMI2
- Bad or corroded terminals or connector at the camshaft position sensor or pump position sensor
- Bad or corroded terminals or connector at the ECU connector, including the 60-way connector
- Open or short in the wiring harness between the sensor and ECU, including shorts to another signal wire
- Loose ground connections
- Loose alternator connections or excessive alternator electrical noise
- Electromagnetic interference (EMI) from an incorrectly installed 2-way radio, radar source, or sensor wiring routed too close to strong electric or magnetic fields
- Burrs, chips, or debris on the camshaft timing wheel, camshaft gearweb faces, inner camshaft gear rear face, or high-pressure pump timing wheel
- Damaged camshaft gear or damaged sensor
- Bad camshaft position sensor or bad pump position sensor
- Water or moisture intrusion in connectors causing intermittent wiring problems
- Short to ground on the sensor return wire
- Bad ECU software or a bad ECU
How to troubleshoot John Deere Engines SPN636FMI2: first checks
- Without disconnecting anything first, visually inspect the ECU connector(s), including the 60-way connector where applicable, and the cam/pump position sensor connector for contamination, corrosion, damage, or terminals that are pushed back or poorly seated
- Trace the wiring harness between the sensor and the ECU looking for chafing, pinched wire, or a signal wire routed close to another signal wire, the alternator, a 2-way radio, or other strong electrical noise sources
- Check for water intrusion in connectors and confirm ground connections at the engine and chassis are clean and tight
- Inspect the alternator and its connections, since alternator electrical noise is a listed cause; a noise test on the alternator circuit may be warranted
- Physically inspect the camshaft timing wheel, camshaft gear, gearweb faces, and inner camshaft gear rear face (or the high-pressure pump timing wheel, depending on engine) for burrs, chips, or debris
- Check whether a crankshaft position sensor code is also active, since that combination prevents the engine from restarting or keeps it stalled until at least one of the two codes is repaired
How the code clears
No separate clearing step is listed beyond repairing the underlying wiring, connector, sensor, or timing wheel problem. Once the fault condition (noise on the signal) is corrected, the code should stop setting on its own; there is no distinct manual reset procedure described.
Frequently asked questions
What does SPN636FMI2 mean on a John Deere engine?
It means the engine control unit detected excessive noise, or extra unexpected pulses, on the camshaft position sensor signal (also referred to as the pump position sensor on some engines). It is a signal-quality fault, not a missing-signal fault.
Will my engine still run with SPN636FMI2 active?
Usually yes. The engine may hesitate or die momentarily when the code sets, but it will typically restart, using the crankshaft position sensor alone to determine piston position. Prolonged cranking time may be needed to get it started again.
Why won't my engine restart at all with this code?
If a crankshaft position sensor trouble code is active at the same time as SPN636FMI2, the ECU loses all reliable position reference and the engine will not start, or will stall and stay stalled, until at least one of the two codes is repaired.
What usually causes the noise on the cam or pump position signal?
Common causes include corroded or loose connector terminals, chafed or shorted wiring, loose ground or alternator connections, electromagnetic interference from a poorly installed 2-way radio or radar source, and physical burrs or debris on the camshaft or pump timing wheel.
Can a bad alternator cause SPN636FMI2?
Yes. Loose alternator connections or excessive alternator electrical noise are both listed as possible causes, so the charging system's connections and noise output are worth checking.
Is SPN636FMI2 the same as SPN636FMI8?
No, they are related but different faults on the same sensor circuit. Some troubleshooting sequences list FMI 8 and FMI 2 together as steps to check in sequence, but this page covers FMI 2 (signal noise/invalid data) specifically.
Do I need to inspect the timing wheel itself?
Yes, it's worth checking. Burrs, chips, or debris on the camshaft timing wheel, camshaft gear faces, or the high-pressure pump timing wheel can generate the extra pulses the ECU interprets as noise.