7 hours ago
The Bobcat 864 and Its Hydraulic Control System
The Bobcat 864 was introduced in the late 1990s as part of Bobcat’s push into the compact track loader market. Designed for versatility and power, the 864 featured a 73-horsepower turbocharged diesel engine and a vertical lift path, making it ideal for grading, lifting, and attachment work. With a rated operating capacity of 2,200 pounds and a hydraulic flow of up to 20 gallons per minute, it quickly became a favorite among contractors and rental fleets.
Bobcat, founded in 1947 in North Dakota, had by the 2000s become synonymous with compact equipment. The 864 was part of a broader lineup that helped Bobcat dominate the skid steer and track loader market, with tens of thousands of units sold globally.
One of the more sophisticated features of the 864 was its electronically controlled hydraulic lockout system, which included spool lock solenoids designed to prevent unintended movement of the lift and tilt functions when the operator was not properly seated or the lap bar was raised.
Understanding the Spool Lock Solenoid Function
The spool lock solenoid is an electrically actuated valve that locks the hydraulic spools in place when the machine is in a non-operational state. This safety feature prevents accidental activation of the loader arms or bucket when the operator exits the cab or fails to engage the lap bar.
Terminology:
Symptoms and Diagnostic Observations
A common symptom of spool lock solenoid failure is the inability to operate the lift or tilt functions unless the lap bar is down before startup. If the operator raises the bar and attempts to restart, the system locks out and displays an error code such as “18-07 Spool Lock Solenoid Open Circuit.”
This behavior suggests that the control module is not receiving the correct resistance or voltage signal from the solenoid circuit. Even after replacing the solenoids, the error may persist if the underlying issue lies in the wiring harness or ECU.
Field Anecdote from Tennessee
A contractor in Chattanooga experienced this issue after swapping the engine in his Bobcat 864. Post-repair, the machine would only operate hydraulics if the lap bar was engaged before turning the key. If the bar was lifted and the machine restarted, the controls locked out again.
After replacing both spool lock solenoids with no improvement, he traced the wiring harness for damage. Despite finding no pinched wires, the error persisted. Eventually, he suspected the ECU itself might be misreading the circuit due to internal faults or voltage irregularities during startup.
Electrical Schematic and Testing Strategy
To diagnose this issue, technicians should follow a structured approach:
Preventive Measures and Long-Term Solutions
To avoid recurring spool lock solenoid issues, operators should adopt the following practices:
The spool lock solenoid open circuit error on the Bobcat 864 is a nuanced electrical fault that often persists despite component replacement. By understanding the interaction between the lap bar, ECU, and solenoid circuit, technicians can isolate the root cause and restore full hydraulic functionality. With proper diagnostics and preventive care, the 864 remains a reliable workhorse capable of tackling demanding jobs across construction, landscaping, and agriculture.
The Bobcat 864 was introduced in the late 1990s as part of Bobcat’s push into the compact track loader market. Designed for versatility and power, the 864 featured a 73-horsepower turbocharged diesel engine and a vertical lift path, making it ideal for grading, lifting, and attachment work. With a rated operating capacity of 2,200 pounds and a hydraulic flow of up to 20 gallons per minute, it quickly became a favorite among contractors and rental fleets.
Bobcat, founded in 1947 in North Dakota, had by the 2000s become synonymous with compact equipment. The 864 was part of a broader lineup that helped Bobcat dominate the skid steer and track loader market, with tens of thousands of units sold globally.
One of the more sophisticated features of the 864 was its electronically controlled hydraulic lockout system, which included spool lock solenoids designed to prevent unintended movement of the lift and tilt functions when the operator was not properly seated or the lap bar was raised.
Understanding the Spool Lock Solenoid Function
The spool lock solenoid is an electrically actuated valve that locks the hydraulic spools in place when the machine is in a non-operational state. This safety feature prevents accidental activation of the loader arms or bucket when the operator exits the cab or fails to engage the lap bar.
Terminology:
- Spool Valve: A hydraulic control valve that directs fluid to actuators based on spool position.
- Solenoid: An electromechanical device that converts electrical energy into linear motion, used to shift the spool valve.
- Open Circuit: An electrical fault where continuity is broken, preventing current flow.
Symptoms and Diagnostic Observations
A common symptom of spool lock solenoid failure is the inability to operate the lift or tilt functions unless the lap bar is down before startup. If the operator raises the bar and attempts to restart, the system locks out and displays an error code such as “18-07 Spool Lock Solenoid Open Circuit.”
This behavior suggests that the control module is not receiving the correct resistance or voltage signal from the solenoid circuit. Even after replacing the solenoids, the error may persist if the underlying issue lies in the wiring harness or ECU.
Field Anecdote from Tennessee
A contractor in Chattanooga experienced this issue after swapping the engine in his Bobcat 864. Post-repair, the machine would only operate hydraulics if the lap bar was engaged before turning the key. If the bar was lifted and the machine restarted, the controls locked out again.
After replacing both spool lock solenoids with no improvement, he traced the wiring harness for damage. Despite finding no pinched wires, the error persisted. Eventually, he suspected the ECU itself might be misreading the circuit due to internal faults or voltage irregularities during startup.
Electrical Schematic and Testing Strategy
To diagnose this issue, technicians should follow a structured approach:
- Inspect all connectors related to the spool lock solenoid for corrosion, bent pins, or loose crimps.
- Use a multimeter to check continuity across the solenoid circuit.
- Measure voltage at the solenoid during key-on and engine-run states.
- Verify ground integrity from the solenoid to chassis ground.
- Check resistance values against factory specifications to confirm ECU interpretation.
Preventive Measures and Long-Term Solutions
To avoid recurring spool lock solenoid issues, operators should adopt the following practices:
- Keep electrical connectors clean and dry using dielectric grease
- Inspect wiring harnesses annually for wear or abrasion
- Replace solenoids with OEM or high-quality aftermarket units
- Avoid rapid key cycling during startup, which can confuse the ECU
- Maintain battery voltage above 12.5V to ensure stable ECU operation
- Install inline fuse protection for solenoid circuits
- Add diagnostic LEDs to confirm solenoid activation
- Retrofit newer control modules with improved fault tolerance
The spool lock solenoid open circuit error on the Bobcat 864 is a nuanced electrical fault that often persists despite component replacement. By understanding the interaction between the lap bar, ECU, and solenoid circuit, technicians can isolate the root cause and restore full hydraulic functionality. With proper diagnostics and preventive care, the 864 remains a reliable workhorse capable of tackling demanding jobs across construction, landscaping, and agriculture.
