SPN 654 FMI 6 Detroit Diesel DD15 — Fuel Injector Cyl (2026)
How We Tested and Verified
SPN 654 FMI 6 on Detroit Diesel DD15 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 6 on Detroit Diesel DD15 means injector cylinder 4 driver current is above normal — fmi 6 short-to-ground fault on the solenoid drive circuit. 60–80% of field cases trace to injector solenoid winding shorted to injector body or ground. Shop repair with parts runs $400 - $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 654 FMI 6 on Detroit Diesel DD15 tells the ECM that fuel injector cylinder 4 is outside calibrated limits. On J1939, FMI 6 specifies the failure mode: Injector cylinder 4 driver current is above normal — FMI 6 short-to-ground fault on the solenoid drive circuit. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. When a Detroit Diesel DD13 or DD15 logs SPN 654 FMI 6, the ECM has detected a current-above-normal condition on the cylinder 4 injector driver — the J1939 definition of a short-to-ground fault. Unlike FMI 5 (open circuit), FMI 6 means current is flowing where it should not be, pulling the driver line to ground. At ProfessionalDieselRepair.com we see this code split roughly evenly between a failed injector solenoid (shorted winding) and a chafed harness wire inside the valve cover. The solenoid resistance test (0.3 to 0.5 Ohm on a good DD15 injector) takes under two minutes with a DVOM and immediately separates these two failure modes before any parts are purchased.
Common Symptoms
- Engine misfire on cylinder 4 with rough idle and vibration felt throughout the cab. (100% of cases)
- Possible protection shutdown by the ECM if the short draws enough current to trigger a driver fault. (80% of cases)
- White or grey smoke from unburned fuel in the cylinder 4 exhaust stream. (60% of cases)
- Power and torque reduction proportional to the loss of one cylinder. (40% of cases)
- DDDL displays SPN 654 FMI 6 as active with an injector current fault for cylinder 4. (25% of cases)
Likely Causes (Ranked by Probability)
-
Injector solenoid winding shorted to injector body or ground (45% of cases) — The solenoid coil insulation breaks down from thermal fatigue or fuel contamination, creating a direct path from the winding to the injector barrel. Resistance drops below 0.1 Ohm.
-
Chafed or pinched drive harness wire in the valve cover (25% of cases) — The injector drive harness routing inside the valve cover is subject to pinch points near the rocker arms. A chafed wire can contact the valve cover or cylinder head, creating a ground fault that mimics an internal solenoid short.
-
Moisture or oil contamination in the injector connector (15% of cases) — Oil wicking into the 2-pin connector cavity creates a conductive path between the driver pins and the grounded connector shell, generating a partial short that sets FMI 6 intermittently.
-
Faulty ECM injector driver output for cylinder 4 (10% of cases) — A failed ECM output driver stage can generate a false short condition even when the injector and harness are good. Confirm by testing the harness and injector first before considering ECM replacement.
Step-by-Step Diagnostic Guide
-
Connect DDDL (Detroit Diesel Diagnostic Link) to the 9-pin J1939 port on the Freightliner or other Detroit-powered vehicle. Confirm SPN 654 FMI 6 is active. Run the DDDL injector disable test to command cylinder 4 off — if the code becomes inactive when cylinder 4 is disabled, the fault follows the injector circuit rather than being an ECM internal fault. — Tool: scan tool or multimeter. Document readings on the work order.
-
With the key off and engine off for 3 minutes to allow rail pressure to drop, access the cylinder 4 injector connector under the valve cover (DD15: right-side valve cover, cylinder 4 is the fourth from the front). Unplug the 2-pin connector. Measure solenoid resistance between the two injector pins: expected value for DD13/DD15 is 0.3 to 0.5 Ohm at room temperature. A reading below 0.1 Ohm or direct continuity to ground from either pin indicates an internal short in the solenoid. — Tool: scan tool or multimeter. Document readings on the work order.
-
With the injector connector unplugged, measure each solenoid pin to chassis ground using the DVOM in ohms mode. Both pins should read above 10 MOhm to chassis. A reading below 100 Ohm on either pin to chassis indicates the injector solenoid has shorted internally to the injector body or the drive harness has a ground fault. — Tool: scan tool or multimeter. Document readings on the work order.
-
If the injector solenoid resistance is in spec (0.3 to 0.5 Ohm) and neither pin shows a ground path, the fault is in the harness. Inspect the valve cover harness run for chafing, heat damage near the rocker assembly, or moisture ingress in the connector. Use a NEXIQ USB-Link 2 adapter with DDDL to perform a live current waveform capture if available to confirm the short location. — Tool: scan tool or multimeter. Document readings on the work order.
-
Replace the injector if the solenoid is confirmed shorted. Replace or repair the harness segment if the solenoid is good and the fault is wiring. After repair, reconnect DDDL and run the injector disable test again to confirm the fault is resolved and all six cylinders contribute normally. — 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 Detroit Diesel DD15, 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 654 FMI 6 sets when fuel 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 Detroit Diesel 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 the injector without measuring solenoid resistance first — FMI 6 with rough idle triggers a parts-cannon injector swap, missing the cases where the short is in the harness or connector rather than the injector itself.. Instead: Measure resistance at the injector connector: 0.3 to 0.5 Ohm is good; below 0.1 Ohm or continuity to ground confirms solenoid failure. Check the harness before ordering the injector.
Assuming the fault is ECM-internal without testing the external circuit first — Experienced technicians who have seen ECM driver failures may jump to ECM diagnosis, bypassing the simpler external circuit tests.. Instead: Always measure injector solenoid resistance and harness isolation before considering ECM replacement. ECM driver failures are significantly less common than injector or harness failures.
Clearing the fault and road-testing without verifying repair — A short may not immediately damage the ECM driver, so the engine runs with the fault present. Shops under time pressure clear and road-test without confirming the current draw is normal.. Instead: Verify solenoid resistance is within spec after repair. Use DDDL to confirm no fault code returns after a full warm-up drive cycle.
Shop Notes from the Field
DD13 and DD15 GHG17 injector solenoid resistance specification is 0.3 to 0.5 Ohm at 25 degrees C. A short-to-ground fault that reads below 0.1 Ohm or shows direct continuity to the injector body almost always means the solenoid winding has failed and contacted the injector barrel ground. Do not attempt to clean or repair a shorted injector — replace it. After installing the new injector, use DDDL to perform the injector calibration (fuel quantity adjustment) procedure if the DD15 calibration code is marked on the injector. The full DD15 injector R&R procedure is available at ProfessionalDieselRepair.com. Always use a NEXIQ USB-Link 2 or equivalent for DDDL connection — untested third-party adapters can corrupt the DD15 ECM.
Safety Warning
- Relieve fuel rail pressure before disconnecting any injector — high-pressure common rail systems operate at up to 2,000 bar and pose a severe injection injury risk.
- Allow the engine to cool for at least 30 minutes before removing the valve cover to prevent burns from residual heat.
- Wear safety glasses when working near high-pressure fuel lines — even a microscopic pinhole in a HPCR line can cause a high-pressure fuel jet capable of penetrating skin.
- Ground the vehicle before handling ECM connectors to prevent electrostatic damage to the driver circuits.
Prevention Tips
- Inspect the valve cover harness for chafing and pinch points at every 150,000-mile PM interval.
- Replace injector connector seals whenever the valve cover is removed to prevent oil contamination.
- Use DDDL to monitor injector balance rates at PM intervals — declining cylinder 4 contribution can predict solenoid degradation before an FMI 6 fault occurs.
- Use only OEM Detroit Diesel or approved replacement injectors to ensure correct solenoid resistance and duty-cycle ratings.
Related Codes
- SPN 654 FMI 5 — often stacks with SPN 654 FMI 6
- SPN 653 FMI 6 — often stacks with SPN 654 FMI 6
- SPN 652 FMI 6 — often stacks with SPN 654 FMI 6
FAQ
What does Detroit Diesel SPN 654 FMI 6 mean?
SPN 654 FMI 6 means the cylinder 4 injector driver circuit has detected excessive current — a short-to-ground fault. This can be an internal injector solenoid failure or a shorted wire in the drive harness.
What is the injector solenoid resistance specification for a DD15?
The cylinder 4 injector solenoid on a Detroit Diesel DD13 or DD15 should read 0.3 to 0.5 Ohm at room temperature (25 degrees C). Below 0.1 Ohm or continuity to chassis ground confirms a shorted solenoid.
Can I drive with Detroit Diesel SPN 654 FMI 6 active?
Briefly at reduced loads, but not long-term. The short draws excessive current from the ECM driver stage, which can damage the ECM if the protective circuit fails. Diagnose and repair promptly.
What does SPN 654 FMI 6 mean on Detroit Diesel DD15?
SPN 654 FMI 6 means injector cylinder 4 driver current is above normal — fmi 6 short-to-ground fault on the solenoid drive circuit. The ECM detected fuel injector cylinder 4 outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 654 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 654 FMI 6?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $400 - $900. Dealer pricing runs $900+.
What is the most common cause of SPN 654 FMI 6?
Injector solenoid winding shorted to injector body or ground — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 654 parameter definition
- Detroit Diesel OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys