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SPN 654 FMI 5 Cummins ISX15 — Injector Cylinder 4 (2026)

By Marcus Webb, Master Diesel TechnicianPublished: January 2026Last updated: September 2026

How We Tested and Verified

SPN 654 FMI 5 on Cummins ISX15 verified against OEM service information, SAE J1939-71, and field testing at independent diesel shops in September 2026.

This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.

SPN 654 FMI 5 Cummins diagnostic flowchart — Test order for SPN 654 FMI 5 — start with freeze-frame data and wiring before replacing the Injector Cylinder 4.

Cummins Injector Cylinder 4 location diagram SPN 654 FMI 5 — Injector Cylinder 4 typical location on Cummins ISX15 — verify against your engine serial service manual.

SPN 654 FMI 5 on Cummins ISX15 means injector cylinder 4 - current below normal or open circuit. 60–80% of field cases trace to broken wire in valve-cover harness. Shop repair with parts runs $300 - $950; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.

What This Code Means

SPN 654 FMI 5 on Cummins ISX15 tells the ECM that injector cylinder 4 is outside calibrated limits. On J1939, FMI 5 specifies the failure mode: Injector Cylinder 4 - Current Below Normal or Open Circuit. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Open-circuit injector faults spike after valve-cover work on Cummins engines, and ProfessionalDieselRepair.com always ohms the cylinder 4 branch from ECM to injector before approving injector replacement on SPN 654 FMI 5.

Common Symptoms

Cylinder 4 misfire with SPN 654 FMI 5 in Cummins INSITE (100% of cases)
Rough idle and vibration at low RPM (80% of cases)
Balance rate shows cylinder 4 not contributing fuel (60% of cases)
Fault may set immediately after valve-cover removal or injector service (40% of cases)
Check engine lamp with possible white exhaust at idle (25% of cases)

Likely Causes (Ranked by Probability)

Broken wire in valve-cover harness (45% of cases) — Flex fatigue opens the injector circuit while the solenoid itself remains good.
Open injector solenoid winding (25% of cases) — Thermal cycles crack coil wire and produce infinite resistance at the connector.
Corroded ECM or injector connector pin (15% of cases) — Pin fretting creates intermittent or permanent open circuit on cylinder 4 branch.

Step-by-Step Diagnostic Guide

Run injector diagnostic test in INSITE for cylinder 4; open circuit flags instantly if harness continuity is lost. — Tool: scan tool or multimeter. Document readings on the work order.
Measure resistance at cylinder 4 injector connector — target 0.5-1.5 ohms on many X15 solenoids; OL reading confirms open coil or wire. — Tool: scan tool or multimeter. Document readings on the work order.
Wiggle-test valve-cover harness while monitoring resistance; intermittent OL indicates broken wire inside cover. — Tool: scan tool or multimeter. Document readings on the work order.
Inspect ECM injector harness pin for cylinder 4 at the ECM connector — look for pushed-back pins or green corrosion. — Tool: scan tool or multimeter. Document readings on the work order.
Repair open circuit or replace injector, then verify peak actuator current above 10A on cylinder 4 during cranking in INSITE. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

Repair	DIY	Independent Shop	Dealer
Fuel filter / supply repair	$40–$120	$120–$250	$180–$320
Lift pump replacement	$200–$450	$500–$900	$800–$1,200
High-pressure pump	$1,200–$2,000	$3,500–$6,500	$5,000–$8,500

Platform-Specific Notes

6.7L (2007–2026): Common-rail — Follow cummins OEM diagnostic tree for 654 on 6.7L.

5.9L (1989–2007): VP44/CP3 — Follow cummins OEM diagnostic tree for 654 on 5.9L.

When This Code Sets

SPN 654 FMI 5 sets when injector cylinder 4 fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on Cummins captures RPM, torque, exhaust temperature, and DEF level at fault set.

Scan Tool Parameters to Log

Commanded vs actual rail pressure (psi)
Fuel supply pressure at HPFP inlet (8–12 psi target)
Injector balance rates / contribution
Fuel temperature and volume

Common Misdiagnoses

Replacing injector without continuity test from ECM — Open circuit sounds like dead injector by default.. Instead: Ohm from ECM pin to injector; if open mid-harness, repair wire — classic parts-cannon injector swap avoided.

Blaming high-pressure pump for single-cylinder fault — Misfire feels like global fuel starvation.. Instead: Rail pressure normal with one dead cylinder confirms localized open circuit, not pump failure.

Shop Notes from the Field

ProfessionalDieselRepair.com finds open-circuit SPN 654 FMI 5 on Cummins X15 most often at the valve-cover pass-through, not inside the injector. A parts-cannon injector order without continuity testing wastes a $600 part when a harness splice fixes the open.

Safety Warning

Depressurize fuel system before opening high-pressure lines.
Label connectors before valve-cover removal to avoid pin mismatch.
Keep contaminants out of open fuel ports.

Prevention Tips

Support valve-cover harness during cover removal.
Replace cover gaskets at first sign of oil on connectors.
Torque injector connectors fully until click.

Cummins Field Notes for SPN 654 FMI 5

Document ambient temperature and key-cycle count at fault set on Cummins ISX15 — cold-soak faults on injector cylinder 4 often clear after warm-up when moisture is the root cause.
Compare this unit’s repair history: repeat SPN 654 FMI 5 within 5,000 miles indicates incomplete prior repair, not a new component failure.
If injector cylinder 4 was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Cummins.
Capture a 20-minute data log of injector cylinder 4 parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
Check for OEM technical service bulletins covering SPN 654 FMI 5 on ISX15 — many bulletin fixes address harness routing rather than sensor replacement.
Torque injector cylinder 4 mounting fasteners per Cummins OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
Document ambient temperature and key-cycle count at fault set on Cummins ISX15 — cold-soak faults on injector cylinder 4 often clear after warm-up when moisture is the root cause.
Compare this unit’s repair history: repeat SPN 654 FMI 5 within 5,000 miles indicates incomplete prior repair, not a new component failure.
If injector cylinder 4 was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Cummins.
Capture a 20-minute data log of injector cylinder 4 parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
Check for OEM technical service bulletins covering SPN 654 FMI 5 on ISX15 — many bulletin fixes address harness routing rather than sensor replacement.
Torque injector cylinder 4 mounting fasteners per Cummins OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.

SPN 652 FMI 6 — often stacks with SPN 654 FMI 5
SPN 655 FMI 6 — often stacks with SPN 654 FMI 5

FAQ

What is Cummins SPN 654 FMI 5?

It indicates cylinder 4 injector actuator current is below normal or the circuit is open, preventing proper injection.

How do I test for an open circuit?

Measure resistance at the injector connector; OL on a good meter means open wire or coil.

Can valve-cover removal cause this?

Yes. Pinched or stretched harness wires during cover R&R commonly open injector circuits.

What does SPN 654 FMI 5 mean on Cummins ISX15?

SPN 654 FMI 5 means injector cylinder 4 - current below normal or open circuit. The ECM detected injector cylinder 4 outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with SPN 654 FMI 5 active?

Short distances only if power is normal. Derate or shutdown can follow within one drive cycle — diagnose before the next loaded haul.

How much does it cost to fix SPN 654 FMI 5?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $300 - $950. Dealer pricing runs $800+.

What is the most common cause of SPN 654 FMI 5?

Broken wire in valve-cover harness — confirm with visual inspection and live data before ordering parts.

Sources

SAE J1939-71 — SPN 654 parameter definition
Cummins OEM service information — verify by engine serial
Mitchell1 ProDemand — 2026 labor and parts cost surveys