Troubleshooting Hydraulic Lockout in the Bobcat 773G BICS System

[MikePhua]

Bobcat’s Skid Steer Legacy and the 773G Platform
Bobcat Company, founded in North Dakota in 1947, revolutionized compact construction machinery with the invention of the skid steer loader in the late 1950s. By the early 2000s, Bobcat had introduced the G-series, including the 773G, which featured improved operator comfort, enhanced hydraulic performance, and the integration of the BICS system—Bobcat Interlock Control System. The 773G, powered by a 46-horsepower Kubota diesel engine and offering a rated operating capacity of 1,750 pounds, became a popular choice for contractors, landscapers, and municipalities. Tens of thousands of units were sold globally, and many remain in active service today.
Terminology Annotation

• BICS (Bobcat Interlock Control System): A safety system that prevents hydraulic and drive functions unless specific conditions are met, such as seat occupancy and lap bar engagement.
  
• Hydraulic Lockout Valve: A solenoid-controlled valve that blocks hydraulic flow until the BICS system authorizes operation.
  
• Solenoid: An electromechanical device that actuates the hydraulic lockout valve when energized.
  
• Seat Switch: A pressure-sensitive switch that detects operator presence and sends a signal to the BICS controller.
  

Symptoms of Hydraulic Lockout Failure
Operators of the 773G may encounter a situation where the machine starts normally, but the lift and tilt functions remain disabled. The engine may load slightly when controls are engaged, but no movement occurs. The LED indicators on the BICS panel may show partial activation—such as the system and traction lights illuminating, while the lift/tilt light remains off or flashes intermittently. This behavior suggests a fault in the interlock circuit or a failure to energize the hydraulic lockout solenoid.
Root Causes and Diagnostic Pathways
Several factors can lead to hydraulic lockout:

• Faulty Seat Switch: If the switch fails to detect operator presence, the BICS system will not enable hydraulics.
  
• Disconnected or Damaged Wiring: The harness connecting the BICS controller to the solenoid may be loose, corroded, or broken.
  
• Failed Solenoid Coil: If the coil is open or shorted, it will not actuate the lockout valve.
  
• Controller Malfunction: The BICS module itself may fail to process input signals correctly.
  
• Low System Voltage: Weak battery or poor ground can prevent proper signal delivery to the solenoid.
  

Anecdote from a Municipal Fleet
In 2019, a city maintenance crew in Ontario reported a 773G that refused to lift or tilt after a battery replacement. After checking fuses and relays, they discovered the seat switch connector had been dislodged during cab cleaning. Reconnecting the switch restored full function. They later added a checklist to their maintenance routine to verify BICS inputs before each shift.
Recommended Diagnostic Steps

• Verify seat switch operation using a multimeter; check for continuity when seated
  
• Inspect lap bar sensor and ensure it engages fully
  
• Check voltage at the solenoid connector; should read 12V when system is active
  
• Test solenoid coil resistance; typical range is 10–20 ohms
  
• Examine wiring harness for abrasion or corrosion near the hydraulic valve block
  
• Reset the BICS controller by disconnecting the battery for 5 minutes
  

Preventative Maintenance Strategies
To avoid future lockout issues:

• Clean and inspect BICS connectors monthly
  
• Replace seat switch every 1,000 hours or if intermittent faults occur
  
• Use dielectric grease on all interlock connectors
  
• Secure wiring harnesses with clamps to prevent vibration damage
  
• Keep a spare solenoid and switch in the service truck for quick replacement
  

Design Reflections and Suggested Improvements
While the BICS system enhances safety, its reliance on multiple sensors and electrical inputs introduces complexity. Future upgrades could include:

• Diagnostic display with fault codes for faster troubleshooting
  
• Redundant sensor pathways to prevent single-point failure
  
• Wireless monitoring of interlock status via mobile app
  
• Improved sealing on connectors to resist moisture and dust
  

Conclusion
Hydraulic lockout in the Bobcat 773G is often caused by faults in the BICS system, particularly involving the seat switch, solenoid, or wiring. With structured diagnostics and preventative care, operators can restore functionality and avoid costly downtime. The 773G remains a reliable and capable machine, but its interlock system demands attention to detail and a proactive maintenance mindset.