Scania SPN 656 FMI 5: Cylinder #6 Injector Circuit Open
SPN 656 FMI 5 (FMI 5) — Engine Injector Cylinder #6 - Current Below Normal or Open Circuit
Quick Answer
SPN 656 FMI 5 means the cylinder #6 injector solenoid circuit is open, causing a misfire on that cylinder. This is a high-severity code with noticeable power loss and rough running - check the harness connector before replacing the injector.
Overview: Scania SPN 656 FMI 5
A dead cylinder on the back end of an inline-six is easy to feel but sometimes harder to access. ProfessionalDieselRepair.com always checks the engine harness connector pins first, since corrosion there mimics an actually failed injector solenoid perfectly.
Repair Snapshot
Time
2 - 4 Hours
Difficulty
Advanced
Parts Cost
$300 - $950
Dealer Labor
$750+
Tools Required
- Scania SDP3
- Jaltest Diagnostic Tool
- Diesel Laptops Scan Tool
- Multimeter
What SPN 656 FMI 5 Means
SPN 656 FMI 5 means the ECM commanded cylinder #6's injector solenoid but detected insufficient current, consistent with an open circuit. On Scania inline engines this causes a noticeable misfire on the affected cylinder, along with rough running and reduced power.
Symptoms Drivers Notice
- Amber or red warning lamp with active misfire on cylinder #6
- Rough idle and noticeable engine shake at low RPM
- Noticeable power loss under load
- Possible white smoke from unburned fuel at the affected cylinder
Most Likely Root Causes
Corroded or bent pin in the engine harness connector
CommonMoisture intrusion or a bent pin at the injector connector interrupts the circuit without the injector itself being defective.
Failed injector solenoid
OccasionalInternal solenoid winding failure directly opens the circuit and requires injector replacement.
Chafed harness wire near the valve cover
OccasionalHeat and vibration exposure over time can wear through insulation, breaking the injector circuit conductor.
Common Misdiagnoses (Don't Waste Parts)
Replacing the injector without checking the harness connector
Why it happens: A parts-cannon assumption that any injector circuit code means the injector itself failed, skipping the cheaper connector inspection.
Do this instead: Inspect and test the harness connector and wiring continuity first - a corroded pin or chafed wire produces the identical fault and is far cheaper to fix.
Master Tech Commentary
Mechanic's Notes
Shop tip: ProfessionalDieselRepair.com always checks the engine harness connector at the injector before condemning the part - a corroded or bent pin in that connector produces the exact same open-circuit fault as a failed injector solenoid.
Step-by-Step Diagnostic Procedure
- Step 1: Pull the fault and freeze-frame data on Scania SDP3 to confirm cylinder #6 is the affected injector.
- Step 2: Inspect the injector #6 connector for corrosion, looseness, or heat damage near the valve cover.
- Step 3: Back-probe the injector solenoid circuit with a multimeter, key on engine off, to check for continuity through the driver circuit.
- Step 4: Measure injector solenoid resistance at the connector and compare against Scania's specification.
- Step 5: Trace the wiring from the injector connector back to the engine harness connector for chafing or a broken conductor.
- Step 6: Replace the injector only after confirming the solenoid itself is open, since a harness break produces the identical fault code.
Professional service / OEM-level scan tools are recommended before clearing this fault for good.
Live Data & Freeze-Frame Tips
Use injector cutout testing on SDP3 to confirm cylinder #6 contributes zero RPM drop when commanded, verifying the misfire location matches the fault code before beginning teardown.
Safety Warnings
- Relieve fuel system pressure before disconnecting any injector or fuel line connections.
- Allow the engine to cool before accessing the injector harness connector.
When to Limp In vs Tow
Towing is not typically necessary, but the engine will run rough and underpowered until repaired - avoid heavy load hauling until the misfire is resolved.
Prevention Tips for Fleets & Owner-Operators
- Inspect harness connectors for corrosion during scheduled valve adjustment services.
- Keep injector connectors clean and protected from moisture intrusion.
- Address any minor injector circuit warnings promptly before they progress to a full open circuit.
Related Fault Codes
SPN 656 FMI 6
Cylinder #6 injector current above normal/shorted - the opposite electrical fault on the same injector circuit.
SPN 652 FMI 5
Cylinder #2 injector open circuit - the same fault pattern on a different cylinder's injector.
Frequently Asked Questions
Can I keep driving with this code active?
Short distances are possible, but expect a rough-running, underpowered engine. Get it repaired soon since running on a dead cylinder increases wear on other components.
How do I reset this code without a scan tool?
You need Scania SDP3 or a comparable tool like Jaltest to clear the code after confirming and repairing the injector circuit.
What triggers a derate on this code?
This code doesn't typically trigger a formal ECM derate, but the misfire itself causes a real, noticeable loss of power and roughness.
Is it always the injector that needs replacing?
No, a corroded connector pin or chafed wire is a common and cheaper cause than an actually failed injector solenoid.
Will this cause white smoke?
Yes, unburned fuel from the non-firing cylinder can produce white smoke, especially noticeable at startup or idle.
How can I confirm which cylinder is affected?
Use an injector cutout test on your diagnostic tool - cutting out a healthy cylinder causes an RPM drop, while cutting out the already-dead cylinder shows no change.