John Deere Engines SPN651FMI5 Fault Code: Injector #1 Circuit Has High Resistance
Also called Cylinder #1 EI Circuit Open, Cylinder #1 EUI Circuit Open, Electronic Unit Pump #1 Circuit Has High Resistance, Injector #1 Spill Valve Circuit Has High Resistance, Injector #4 Circuit Has High Resistance
Injector #1 Circuit Has High Resistance · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 651 FMI 5 means the ECU has found an open circuit or high resistance in the cylinder #1 injector circuit, whether that engine uses electronic unit injectors (EUI), electronic injectors (EI), or a common-rail injector setup. When it sets, cylinder #1 will not fire and the engine runs on the remaining cylinders while the ECU tries to keep controlling the engine normally.
Medium severity. The alarm level is listed as Warning and the ECU keeps trying to control the engine normally, but a dead or misfiring cylinder #1 means rough running, power loss, and possible long-term wear from unburned fuel or uneven combustion. Diagnose before extended operation, don't ignore it for days.
What does John Deere Engines error code SPN651FMI5 mean?
This code covers the injector circuit for cylinder #1 across several John Deere engine families. On 10.5 L and 12.5 L engines, fuel is delivered by electronic unit injectors (EUIs), which combine the injection pump and injector in one unit mounted in the cylinder head. On the 8.1 L engine, electronic injectors (EIs) get high pressure fuel from a common rail and are switched by a Two-Way Valve (TWV). On other listed engines the ECU shares a common high voltage supply across all injectors and switches the low side (ground) individually for each cylinder.
In every version, the ECU controls injection timing and fuel quantity by opening and closing the injector's internal valve through its ground circuit. SPN 651 FMI 5 means the ECU has detected an open circuit, or in some versions, a few extra ohms of resistance, somewhere in the #1 injector's wiring, connector, or the injector itself.
When the code is active, cylinder #1 will not fire. Depending on the engine, an open in the shared high voltage supply line can also trigger similar high-resistance codes on other injector circuits at the same time, so check neighboring cylinders' codes too.
Common causes of SPN651FMI5
- Bad terminals or connector at the ECU
- Bad terminals or connector at the EUI, EI, or injector harness connector
- Bad #1 injector, EUI, or EI solenoid/TWV
- Bad injector wiring harness, including the harness inside the cylinder head
- Open or short in the harness between the ECU and the injector, including the 90V circuit on EI-equipped engines
- Bad ECU or bad ECU software
- Bad connection specifically at the 12-way (6.8L) or 6-way (4.5L) connector on some engine families
How to troubleshoot John Deere Engines SPN651FMI5: first checks
- Visually inspect the 48-way ECU connector and the injector harness connector at the back or side of the cylinder head for dirty, damaged, bent, or poorly seated terminals
- Check the injector wiring harness for chafing, pinched wire, or damage anywhere between the ECU and the injector
- On EI-equipped 8.1 L engines, check the 90V circuit and main harness for opens or shorts
- If using Service ADVISOR's Harness Diagnostic Mode Test, confirm fuel rail pressure is below 5 MPa (725 psi) before running the test since that is a listed condition for the DTC to display during that test
- Check for other active injector circuit codes at the same time since an open in the shared high voltage supply can affect multiple cylinders, and review the troubleshooting sequence which lists SPN 627 FMI 1 before SPN 651 FMI 5
- Inspect the #1 injector itself and its connector for corrosion or damage if wiring and ECU connections check out
How the code clears
No separate clearing step is listed. Repair the open circuit, high-resistance connection, or faulty component identified during troubleshooting, then verify the code does not return during cranking or running, since that is when the ECU actively checks this circuit.
Frequently asked questions
What does SPN 651 FMI 5 mean on a John Deere engine?
It means the ECU detected an open circuit or high resistance in the cylinder #1 injector circuit. Depending on the engine family, this affects the EUI, EI, or common-rail injector for cylinder #1, and that cylinder will not fire while the code is active.
Can I keep running the engine with this code active?
The alarm level is listed as Warning and the ECU will attempt to control the engine normally, but with cylinder #1 not firing you'll have rough running and reduced power. It's best to diagnose and repair as soon as practical rather than run it long term.
Where should I look first for this fault?
Start with a visual inspection of the ECU connector and the injector harness connector at the cylinder head. Look for dirty, damaged, or poorly positioned terminals, since that's the first action listed for this code across engine families.
Why would multiple injector circuit codes show up at once?
The ECU supplies a shared high voltage line to all injectors and only switches the ground side per cylinder. An open circuit in that shared supply line can trigger high-resistance codes on more than one injector circuit at the same time, not just cylinder #1.
Does fuel rail pressure matter when testing this code?
Yes, on engines using the Harness Diagnostic Mode Test in Service ADVISOR, the DTC may display during that test only if fuel rail pressure is below 5 MPa (725 psi).
Is there a related code I should check alongside SPN 651 FMI 5?
Yes, the listed troubleshooting sequence includes SPN 627 FMI 1 before SPN 651 FMI 5, so check that code as part of your diagnosis.
Could this be an ECU problem instead of a wiring or injector problem?
It's possible. Bad terminals or connectors at the ECU, a bad ECU, or bad ECU software are all listed as possible causes, though wiring and injector issues are checked first since they're more common and easier to inspect.