Injector Cylinder 6 Circuit Open (J1939)
What does VOLVO-MACK-SPN656-FMI5 mean?
The VOLVO-MACK-SPN656-FMI5 (Volvo/Mack D/MP Series) diesel fault code means: Injector Cylinder 6 Circuit Open (J1939). This is a serious severity code.
Common Symptoms
- Check Engine Light illuminated
- Possible engine derate
- Warning message on driver display
- System-specific warning lamp (DPF/DEF/coolant/etc.)
Probable Causes (Ranked by Likelihood)
- Open injector solenoid or cracked coil wire at the valve cover pass-through Very Likely
- Oil contamination at the valve-cover connector (leaking seal) Likely
- ECM injector driver output fault Possible
- Harness chafe damage from valve cover vibration Possible
- Injector internal failure (mechanical stuck) Less Likely
Step-by-Step Diagnostic Procedure
Connect Volvo PTT or Mack Guided Diagnostics and run injector cutout / balance test for all cylinders.
Measure resistance of the injector coil at the valve cover connector (spec per service manual).
Remove the valve cover and inspect the pass-through connector for oil contamination, cracking, or arcing.
Swap the injector harness between cylinders; if the fault follows the harness, replace the harness.
If harness is clean and coil reads out of spec, replace the injector and program the new trim codes.
After any injector replacement, program injector trim via Volvo PTT or Mack Guided Diagnostics.
Frequently Asked Questions
What does Volvo/Mack code SPN656-FMI5 mean?
Volvo/Mack code SPN656-FMI5 (Injector Cylinder 6 Circuit Open (J1939)) is a serious-severity diagnostic trouble code set on D11/MP7, D13/MP8, and D16/MP10 diesel engines in Volvo VNL/VNR and Mack Anthem/Pinnacle/Granite/Titan trucks. It indicates a fault in the fuel injector system and should be read with Volvo Premium Tech Tool (PTT) or Mack Guided Diagnostics.
Can I drive a Volvo or Mack truck with code SPN656-FMI5?
Short distances may be acceptable to reach a repair facility, but the fault will escalate to derate (typically 55 mph then 5 mph on aftertreatment faults). Do not defer diagnosis beyond a shift.
How much does it cost to fix Volvo/Mack code SPN656-FMI5?
Typical repair falls in the range $400-$2,500. Sensor/wiring repairs are at the low end; EGR cooler, NOx sensor set, DEF pump, injector, or head work runs at the high end. Volvo PTT or Mack Guided Diagnostics is normally required for calibration and parameter programming.