John Deere Engines SPN656FMI6 Fault Code: Injector #6 Circuit Has Low Resistance
Also called Cylinder #6 EI Circuit Shorted, Cylinder #6 EUI Circuit Shorted, Injector #6 Spill Valve Circuit Has Low Resistance
Injector #6 Circuit Has Low Resistance · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 656 FMI 6 means the ECU detected a short or low resistance in the cylinder #6 injector circuit, whether that is an electronic unit injector (EUI), electronic injector (EI), or common rail injector depending on the engine. When it sets, cylinder #6 will not fire and the engine runs on the remaining cylinders.
Medium severity. The alarm level is listed as Warning and the ECU will attempt to control the engine in a normal manner. However, running with one dead injector causes an unbalanced, rough-running engine and should be diagnosed promptly rather than ignored.
What does John Deere Engines error code SPN656FMI6 mean?
SPN 656 FMI 6 covers John Deere engines that use electronic unit injectors (EUI), electronic injectors (EI) fed by a high pressure common rail, or common rail electronic injectors depending on the engine family (10.5L, 12.5L, 8.1L, 6.8L, or 4.5L). In every case, fuel delivery for cylinder #6 is controlled by the ECU switching a ground circuit on and off to energize a solenoid, spill valve, or two-way valve inside the injector.
On EUI and EI engines, power to cylinders 4, 5, and 6 is supplied by a shared common wire, while the ECU controls each injector individually by opening and closing its own ground circuit. On common rail engines, the ECU has two internally-connected terminals that supply shared high voltage to all injectors, and the ECU switches the low side (ground) to fire each injector.
This fault sets when the ECU detects a short, or in some descriptions low resistance, in the cylinder #6 injector circuit. When it sets, cylinder #6 will not fire on EUI and EI engines. On common rail engines, a wire-to-wire short between two injectors' low side wiring can cause both injectors to show active low resistance codes at the same time, and a shorted injector coil (windings shorted together) can also cause this code by itself.
What triggers a John Deere Engines SPN656FMI6 code?
The DTC is displayed while the engine is cranking or running and the error condition is active. On common rail engines, it may also be displayed during the Harness Diagnostic Mode Test in Service ADVISOR, provided fuel rail pressure is below 5 MPa (725 psi).
Common causes of SPN656FMI6
- Bad terminals or connector at the ECU (48-way connector on EUI engines)
- Bad terminals or connector at the EUI or EI harness connector, or at the 12-way (6.8L) or 6-way (4.5L) injector connector
- Bad #6 injector (EUI, EI solenoid, or common rail injector), including low coil resistance from shorted windings
- Bad injector wiring harness, including the EUI harness located in the cylinder head
- Open or short in the harness between the ECU and the injector harness, including the 90V circuit or main harness on EI engines
- Wire-to-wire short between the low side wiring of two injectors, which can trigger low resistance codes on both circuits at once
- Bad ECU or bad ECU software
How to troubleshoot John Deere Engines SPN656FMI6: first checks
- Visually inspect the ECU connector (48-way on EUI engines) for dirty, damaged, bent, or poorly seated terminals
- Inspect the injector harness connector for cylinder #6, located at the back of the cylinder head on EUI engines or at the side of the cylinder head on EI engines, for contamination, damage, or poor positioning
- Check all connectors in between the ECU and the injector harness for corrosion, looseness, or physical damage
- Inspect the wiring harness itself for chafing, pinched sections, or damage that could cause a short between wires, especially between the low side wires of adjacent injectors
- On common rail engines, check for low coil resistance at the #6 injector, and check whether a second injector is also showing an active low resistance code, which points to a wire-to-wire short rather than two failed injectors
How the code clears
No separate clearing step is listed. The ECU will attempt to control the engine in a normal manner while the code is active. Repair the underlying wiring, connector, injector, or ECU issue identified during diagnosis, then verify the code does not return during cranking or running.
Frequently asked questions
What does SPN 656 FMI 6 mean on a John Deere engine?
It means the ECU detected a short, or on some engines a low resistance condition, in the cylinder #6 injector circuit. Depending on the engine, this circuit controls an electronic unit injector (EUI), an electronic injector (EI), or a common rail electronic injector.
Will the engine still run with SPN 656 FMI 6 active?
Yes, but cylinder #6 will not fire on EUI and EI engines, so the engine runs unbalanced on the remaining cylinders. The alarm level is listed as Warning, and the ECU will attempt to control the engine in a normal manner.
Can a bad connector cause this code instead of a bad injector?
Yes. Bad terminals or connectors at the ECU, at the injector harness connector, or anywhere in the harness between them are listed as possible causes, so a full inspection of connectors should come before replacing the injector.
Why would two injector circuits show low resistance codes at the same time?
A wire-to-wire short between the low side wiring of two injectors can cause both circuits to show active low resistance DTCs simultaneously. If cylinder #6 and another cylinder both show this code, check for a short between their wiring before condemning either injector.
Is there a fuel pressure condition tied to this code showing up in Service ADVISOR?
On common rail engines, the DTC may display during the Harness Diagnostic Mode Test in Service ADVISOR only if fuel rail pressure is below 5 MPa (725 psi).
Does this code apply to both mechanical unit injector and common rail engines?
Yes. The same SPN 656 FMI 6 code covers EUI engines (10.5L and 12.5L), EI engines (8.1L), and common rail injector systems (6.8L and 4.5L), though the exact injector hardware and connector locations differ between them.