SPN 655 FMI 5 – Injector Cylinder #5 Needle Control Valve, Circuit Open Fault Code (Symptoms, Causes & Fix)
The SPN 655 FMI 5 fault code indicates an open circuit condition in the injector needle control valve for cylinder #5. This diesel engine fault code is triggered when the Engine Control Module (ECM) detects a lack of electrical continuity in the circuit responsible for controlling the injector needle, which can affect fuel delivery and engine performance.
What SPN 655 FMI 5 Means
SPN 655 FMI 5 is a diagnostic trouble code that points to an electrical issue within the fuel injection system, specifically involving the needle control valve of injector cylinder #5. The ECM monitors the circuit for continuity and, upon detecting an open circuit, logs this fault code. This can result from wiring issues, connector problems, or a malfunctioning injector.
Common Causes of This Fault Code
- Open circuit in the injector wiring harness
- Faulty injector needle control valve
- Corroded or damaged connector pins
- ECM malfunction or software issue
- Voltage supply issues to the injector
Symptoms Drivers May Notice
When the SPN 655 FMI 5 fault code is active, drivers may experience rough idling, reduced engine performance, or increased fuel consumption. In some cases, the engine may enter a derate mode to prevent further damage, leading to decreased power output.
How Technicians Diagnose This Fault
Technicians begin diagnosing this fault with a visual inspection of the wiring harness and connectors for any signs of damage or corrosion. Using a multimeter, they check for continuity in the injector circuit to confirm an open circuit condition. Voltage reference and ground circuits are also verified to ensure proper power supply. Diagnostic tools are used to perform an injector actuation test, and ECM data is reviewed for any anomalies that might indicate a software or hardware issue.
Common Misdiagnosis
A common mistake is assuming a mechanical injector failure without conducting thorough electrical testing. Replacing the injector without checking the wiring harness or overlooking potential ECM software issues can lead to unnecessary repairs and persistent faults.
Can You Keep Driving?
While it may be possible to continue driving with the SPN 655 FMI 5 fault code active, it is not advisable. The fault can lead to engine derate or protection mode, reducing power and potentially causing further engine damage if not addressed promptly.
Mechanic's Diagnostic Tip
Always verify the integrity of the wiring harness and connectors before replacing any components. A simple continuity test can save time and prevent unnecessary part replacements. Ensure all connectors are clean and secure to avoid intermittent electrical issues.
Frequently Asked Questions
What does SPN 655 FMI 5 indicate? It indicates an open circuit in the injector needle control valve for cylinder #5.
Can a faulty ECM cause this fault code? Yes, an ECM malfunction or software issue can contribute to this fault.
Is it safe to drive with this fault code? Driving is possible but not recommended due to potential engine derate and performance issues.
