John Deere Engines SPN656FMI5 Fault Code: Injector #6 Circuit Has High Resistance
Also called Cylinder #6 EI Circuit Open, Cylinder #6 EUI Circuit Open, Injector #6 Spill Valve Circuit Has High Resistance
Injector #6 Circuit Has High Resistance · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 656 FMI 5 means the ECU has detected an open circuit or high resistance in the cylinder #6 injector circuit, whether that's an EUI (electronic unit injector), EI (electronic injector), or common rail injector depending on engine family. When this code sets, cylinder #6 will not fire, causing rough running, power loss, or misfire-type symptoms.
Medium severity. The engine keeps running because the ECU continues to control the other cylinders in a normal manner, but cylinder #6 will not fire, which causes rough running, power loss, and increased vibration. This should be diagnosed promptly to avoid extended running on 5 cylinders, but it is not an immediate shutdown situation on most applications.
What does John Deere Engines error code SPN656FMI5 mean?
SPN 656 FMI 5 points to the fuel injection circuit for cylinder #6. Depending on which John Deere engine you have, this circuit could be an EUI (electronic unit injector) used on 10.5 L and 12.5 L engines, an EI (electronic injector) used on the 8.1 L engine, or a common rail electronic injector used on other displacement engines like the 6.8 L or 4.5 L. In every case, the ECU controls fuel delivery by switching the ground side of the injector circuit on and off, and it has detected either a complete open in that circuit or added resistance that is too high for normal operation.
On EUI and EI systems, cylinders 1, 2, and 3 share one power wire and cylinders 4, 5, and 6 share a different power wire, with the ECU switching each individual injector's ground circuit to fire it. When FMI 5 sets for cylinder #6, that individual ground circuit is open, so the ECU cannot energize the injector solenoid or valve, and the cylinder will not fire.
On common rail systems, the ECU provides a shared high voltage supply to all injectors internally, then switches the low side (ground) for each injector individually. FMI 5 on this style can be caused by an open circuit or by just a few ohms of extra series resistance anywhere in the injector #6 circuit, not necessarily a dead short or full open.
What triggers a John Deere Engines SPN656FMI5 code?
The ECU sets this code when it detects an open in the Cylinder #6 EUI or EI circuit, or high resistance in the cylinder #6 electronic injector circuit, while the engine is cranking or running and the error condition is active. On common rail applications, the code may also display during Harness Diagnostic Mode Test in Service ADVISOR, provided fuel rail pressure is below 5 MPa (725 psi).
Common causes of SPN656FMI5
- Bad terminals or connector at the ECU (48-way connector on EUI systems, or the ECU connector on other systems)
- Bad terminals or connector at the EUI/EI harness connector, located at the back or side of the cylinder head, or at the 12-way (6.8 L) or 6-way (4.5 L) connector on common rail systems
- Open or short in the harness between the ECU and the injector harness connector
- Bad #6 injector itself (EUI, EI solenoid, or common rail injector)
- Bad injector wiring harness or bad EUI/EI harness in the cylinder head
- Open or short in the 90V circuit (on EI-equipped 8.1 L engines)
- Bad ECU or bad ECU software
How to troubleshoot John Deere Engines SPN656FMI5: first checks
- Perform a visual inspection of the ECU connector, the injector harness connector at the cylinder head, and any connectors in between. Look for dirty, damaged, corroded, or poorly seated terminals.
- Check the injector wiring harness for chafing, cuts, or damage anywhere between the ECU and the cylinder head, since even a few ohms of added resistance can trigger this code on common rail systems.
- Inspect the shared power wire feeding cylinders 4, 5, and 6 on EUI and EI systems, since a problem here can affect multiple cylinders, not just #6.
- If available, run the Harness Diagnostic Mode Test in Service ADVISOR, keeping in mind fuel rail pressure needs to be below 5 MPa (725 psi) for the test to properly display this DTC on common rail engines.
- Check for other active injector circuit high resistance codes, since an open circuit in the injector high voltage supply can cause multiple injector circuits to show high resistance faults at once.
How the code clears
No separate clearing step is listed. Once the open circuit or high resistance condition is repaired, whether that means cleaning and reseating connector terminals, repairing or replacing damaged harness wiring, or replacing a faulty injector or ECU, the code should clear on its own once the ECU no longer detects the fault condition during normal cranking or running operation.
Frequently asked questions
What does SPN 656 FMI 5 mean on a John Deere engine?
It means the ECU has detected an open circuit or high resistance in the cylinder #6 injector circuit. Depending on your engine, this affects an EUI, EI, or common rail electronic injector, and cylinder #6 will not fire while the fault is active.
Can I keep running the engine with this code active?
The ECU will attempt to control the engine in a normal manner, but cylinder #6 will not fire, so expect rough running, reduced power, and possible vibration. It's best to diagnose and repair the fault as soon as practical rather than running for extended periods on fewer cylinders.
Where should I start looking for the problem?
Start with a visual inspection of the ECU connector and the injector harness connector at the cylinder head. Dirty, damaged, or poorly seated terminals are common causes, along with harness damage between the ECU and the injector.
Why does this code sometimes affect other injector circuits too?
On common rail systems, the ECU supplies shared high voltage internally to all injectors before switching each ground individually. An open in that shared high voltage supply can trigger high resistance codes on injector #6 and other cylinders at the same time.
Is there a specific troubleshooting order for this code?
On common rail applications, the listed troubleshooting sequence checks SPN 627 FMI 1 before SPN 656 FMI 5, since a fault in the shared supply circuit covered by SPN 627 can cause or mask the injector-specific fault.
Does this code require a special reset procedure?
No reset procedure is listed for this code. Once the underlying open circuit, high resistance connection, harness damage, injector, or ECU issue is repaired, the fault condition should stop being detected during normal engine operation.