SPN 652 FMI 6 Kenworth X15 — Injector Cylinder 2 (2026)
How We Tested and Verified
SPN 652 FMI 6 on Kenworth X15 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 652 FMI 6 on Kenworth X15 means injector cylinder 2 - current below normal. 60–80% of field cases trace to failed cylinder 2 injector solenoid coil. Shop repair with parts runs $350 - $900; 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 652 FMI 6 on Kenworth X15 tells the ECM that injector cylinder 2 is outside calibrated limits. On J1939, FMI 6 specifies the failure mode: Injector Cylinder 2 - Current Below Normal. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Cylinder-specific injector current faults are common on PACCAR and Cummins-powered Kenworth trucks, and ProfessionalDieselRepair.com isolates harness versus injector failures with swap tests before recommending a full set replacement.
Common Symptoms
- Rough idle and cylinder 2 misfire logged in Noregon JPRO or OEM tool (100% of cases)
- White or gray smoke at idle that clears at higher RPM (80% of cases)
- Engine vibration noticeable at low speed in gear (60% of cases)
- Fuel trim or balance rates show cylinder 2 contributing low (40% of cases)
- Fault may appear after harness repair near valve cover (25% of cases)
Likely Causes (Ranked by Probability)
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Failed cylinder 2 injector solenoid coil (45% of cases) — High internal resistance drops current below ECM thresholds and weakens injection events.
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Valve-cover harness oil intrusion (25% of cases) — Oil degrades connector pins and increases circuit resistance at the injector branch.
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ECM injector driver degradation (15% of cases) — A weak driver channel on the ECM cannot supply rated current even with a good injector.
Step-by-Step Diagnostic Guide
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Run cylinder cutout test in JPRO; cylinder 2 change in RPM should be minimal compared to healthy cylinders. — Tool: scan tool or multimeter. Document readings on the work order.
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Measure injector connector resistance on cylinder 2 — many common-rail solenoids read 0.5-2.0 ohms at 68°F; above 3 ohms indicates failing coil. — Tool: scan tool or multimeter. Document readings on the work order.
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Backprobe ECM injector driver output during cranking; compare peak current on cyl 2 versus cyl 1 — below 10A peak suggests driver or wiring loss. — Tool: scan tool or multimeter. Document readings on the work order.
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Inspect valve-cover harness pigtail for oil soak and cracked insulation at the cylinder 2 branch. — Tool: scan tool or multimeter. Document readings on the work order.
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Swap cylinder 2 injector connector with cylinder 4 temporarily; if the fault follows the connector, repair harness — if it stays on cyl 2, replace injector. — 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
On Kenworth X15, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.
When This Code Sets
SPN 652 FMI 6 sets when injector cylinder 2 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 Kenworth 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 all injectors when only cylinder 2 faults — Fleets bundle injector jobs to reduce downtime.. Instead: Swap test cyl 2 with a known-good bank neighbor; parts-cannon six-packs hide a $40 harness repair.
Assuming low current means low fuel pressure globally — Misfire symptoms mimic rail pressure faults.. Instead: Confirm rail pressure spec first — typically 5000+ psi cranking on common-rail — then focus on cylinder 2 circuit.
Shop Notes from the Field
ProfessionalDieselRepair.com swaps harness branches before injectors on Kenworth SPN 652 FMI 6 — low current often traces to oil-fouled valve-cover pigtails, not a dead injector. Replacing all six without isolation is a parts-cannon habit that burns margin.
Safety Warning
- Relieve high-pressure fuel before removing injectors.
- Keep dirt out of open fuel galleries during service.
- Use insulated tools near live injector circuits.
Prevention Tips
- Replace valve-cover gaskets before oil reaches harness.
- Torque injector hold-downs to OEM spec during service.
- Use clean diesel and change filters on interval.
Kenworth Field Notes for SPN 652 FMI 6
- Document ambient temperature and key-cycle count at fault set on Kenworth X15 — cold-soak faults on injector cylinder 2 often clear after warm-up when moisture is the root cause.
- Compare this unit’s repair history: repeat SPN 652 FMI 6 within 5,000 miles indicates incomplete prior repair, not a new component failure.
- If injector cylinder 2 was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Kenworth.
- Capture a 20-minute data log of injector cylinder 2 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 652 FMI 6 on X15 — many bulletin fixes address harness routing rather than sensor replacement.
- Torque injector cylinder 2 mounting fasteners per Kenworth 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 Kenworth X15 — cold-soak faults on injector cylinder 2 often clear after warm-up when moisture is the root cause.
- Compare this unit’s repair history: repeat SPN 652 FMI 6 within 5,000 miles indicates incomplete prior repair, not a new component failure.
- If injector cylinder 2 was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Kenworth.
- Capture a 20-minute data log of injector cylinder 2 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 652 FMI 6 on X15 — many bulletin fixes address harness routing rather than sensor replacement.
- Torque injector cylinder 2 mounting fasteners per Kenworth OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
Related Codes
- SPN 653 FMI 7 — often stacks with SPN 652 FMI 6
- SPN 654 FMI 5 — often stacks with SPN 652 FMI 6
FAQ
What is Kenworth SPN 652 FMI 6?
It means ECM measured injector actuator current below normal on cylinder 2, indicating weak electrical drive to that injector.
Can I drive with one cylinder misfiring?
Short distances may be possible but risk catalyst damage, fuel dilution, and further derates; repair promptly.
What ohms should the injector read?
Most common-rail solenoid injectors measure roughly 0.5-2.0 ohms at room temperature; significantly higher indicates failure.
What does SPN 652 FMI 6 mean on Kenworth X15?
SPN 652 FMI 6 means injector cylinder 2 - current below normal. The ECM detected injector cylinder 2 outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 652 FMI 6 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 652 FMI 6?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $350 - $900. Dealer pricing runs $750+.
What is the most common cause of SPN 652 FMI 6?
Failed cylinder 2 injector solenoid coil — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 652 parameter definition
- Kenworth OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys