Troubleshooting SPN 695 FMI 6 Fault Code in Heavy Equipment

[MikePhua]

Understanding SPN and FMI Diagnostic Codes
Modern heavy equipment relies on electronic control modules (ECMs) to monitor and regulate engine and drivetrain performance. When a fault occurs, the system logs diagnostic codes using the SAE J1939 protocol. These codes consist of two parts:

• SPN (Suspect Parameter Number): Identifies the specific system or component involved.
  
• FMI (Failure Mode Identifier): Describes the nature of the fault.
  

SPN 695 refers to the “Engine Override Control Mode,” a parameter that monitors whether the engine is operating under an override condition—typically triggered by limp mode, derate, or manual intervention. When paired with FMI 6, the fault indicates that the current in the override control circuit is above the normal range.
Terminology notes:

• Override Control Mode: A state where the ECM limits or modifies engine behavior due to a fault or manual override.
  
• FMI 6: Indicates “current above normal,” often pointing to a short circuit, failed driver, or excessive load on the control line.
  

Common Causes of SPN 695 FMI 6
This fault code can be triggered by several underlying issues:

• Shorted wiring in the override control circuit
  
• Failed ECM driver transistor
  
• Corroded or loose connectors causing resistance spikes
  
• Aftermarket modifications interfering with control logic
  
• Faulty override switch or relay
  

In one case from a mining site in Nevada, a haul truck began derating unexpectedly. The SPN 695 FMI 6 code was logged, and technicians traced the issue to a damaged harness near the firewall. The insulation had worn through, allowing the control wire to intermittently short against the chassis.
Diagnostic Procedure and Tools
To resolve SPN 695 FMI 6, a structured diagnostic approach is essential. Recommended steps include:

• Retrieve full fault code history using a J1939-compatible scan tool
  
• Inspect wiring harnesses for abrasion, corrosion, or pinched sections
  
• Test voltage and current at the override control pin using a multimeter
  
• Check ECM output driver resistance and continuity
  
• Verify override switch function and relay operation
  

Suggested tools:

• Digital multimeter with amp clamp
  
• OEM-specific diagnostic software (e.g., CAT ET, Cummins Insite, Detroit DiagnosticLink)
  
• Wiring diagrams and pinout charts
  
• Insulation resistance tester for high-voltage circuits
  

In Australia, a fleet technician used a thermal imaging camera to detect a hot spot in the override circuit. The elevated temperature revealed a failing relay that was drawing excessive current, triggering the FMI 6 fault.
Repair Strategies and Component Replacement
Once the fault source is identified, repairs may involve:

• Replacing damaged wiring with OEM-grade shielded cable
  
• Installing new override relays or switches
  
• Reprogramming the ECM if override logic has been corrupted
  
• Updating software to the latest calibration version
  
• Adding protective conduit or sleeving to vulnerable harness sections
  

Terminology notes:

• Driver circuit: The ECM’s internal transistor or logic gate that controls current flow to a component.
  
• Calibration file: Software configuration loaded into the ECM to define operating parameters and fault thresholds.
  

In Canada, a forestry contractor resolved recurring SPN 695 faults by replacing the override switch with a sealed marine-grade toggle. The original switch had corroded internally due to moisture ingress, causing intermittent overcurrent.
Preventive Measures and Long-Term Monitoring
To prevent future SPN 695 FMI 6 faults:

• Conduct quarterly harness inspections, especially near high-vibration zones
  
• Use dielectric grease on connectors to prevent corrosion
  
• Avoid splicing into control circuits for aftermarket accessories
  
• Log override activations and correlate with operating conditions
  
• Train operators to report derate events promptly
  

In Texas, a municipal fleet added override circuit monitoring to their telematics system. When current exceeded preset thresholds, alerts were sent to maintenance staff before faults escalated.
Real-World Anecdotes and Lessons Learned
In South Africa, a quarry loader repeatedly entered limp mode during peak shifts. The SPN 695 FMI 6 code was logged, but no visible damage was found. After extensive testing, the fault was traced to a poorly grounded ECM bracket. Once the ground was reinforced, the issue disappeared.
In Poland, a snowplow operator noticed sluggish throttle response and flashing warning lights. The override control circuit had been compromised by salt corrosion. After rewiring and sealing the connectors, the machine returned to full service.
Conclusion
SPN 695 FMI 6 is more than a nuisance—it’s a signal that the override control system is under electrical stress. Whether caused by wiring faults, component failure, or environmental damage, this code demands careful attention. With proper diagnostics, quality repairs, and preventive strategies, operators can restore full engine functionality and avoid costly downtime.