Diagnosing Hydraulic Lockout on the Bobcat 773: A Deep Dive into BICS and Lift/Tilt Failures

[MikePhua]

Overview
The Bobcat 773 skid steer loader is a robust and widely used machine in construction and agriculture. However, like many compact loaders, it relies heavily on electronic interlock systems to manage hydraulic functions. One of the most perplexing issues operators encounter is the failure of lift and tilt functions despite normal engine and drive performance. This article explores the intricacies of the Bobcat Interlock Control System (BICS), common failure points, diagnostic strategies, and real-world anecdotes that shed light on troubleshooting hydraulic lockout.
Understanding the BICS System
The Bobcat Interlock Control System (BICS) is designed to prevent unintended hydraulic movement unless specific safety conditions are met. It monitors inputs from:

• Seat Switch: Detects operator presence
  
• Lap Bar Sensor: Confirms the safety bar is lowered
  
• Enable Button (if equipped): Activates hydraulic functions
  
• BICS Controller: Processes inputs and sends voltage to unlock solenoids
  

When functioning correctly, the BICS system energizes a solenoid on the hydraulic control valve, allowing lift and tilt operations. If any input is missing or the controller fails, the system remains locked.
Terminology Clarified

• Hydraulic Lockout Valve: A solenoid-controlled valve that blocks hydraulic flow to lift/tilt cylinders unless energized
  
• BICS Solenoid: The coil that receives voltage from the controller to unlock the hydraulic valve
  
• Main Control Valve: The central hydraulic manifold where solenoids and spool valves are mounted
  
• LED Indicators: Lights on the BICS panel that show system status and faults
  

Common Symptoms and Root Causes
Operators often report the following:

• Machine drives normally, but lift/tilt functions are dead
  
• Engine loads up when attempting to lift or tilt, but no movement occurs
  
• BICS panel shows all lights except the lift/tilt LED
  
• No flashing fault indicators, suggesting silent failure
  

These symptoms typically point to one of the following:

• Faulty BICS controller
  
• Disconnected or damaged wiring harness to the solenoid
  
• Failed solenoid coil
  
• Corroded connector pins
  
• Disabled or malfunctioning seat switch
  

Field Anecdote: The Forest Breakdown
A Bobcat 773 parked in a forest for a month refused to move upon restart. The operator suspected a BICS failure and bypassed the traction solenoid to relocate the machine. Later, they attempted to locate the hydraulic lockout solenoid but found multiple auxiliary solenoids instead. This confusion highlights the variability in control valve configurations across model years and the importance of visual confirmation.
Historical Evolution of Lockout Systems
Early C-series Bobcats used mechanical plungers to lock foot pedals. Dropping the lap bar physically depressed these plungers, unlocking hydraulic functions. Later models transitioned to electronic solenoids controlled by the BICS system. This shift improved safety but introduced diagnostic complexity. The transition reflects a broader industry trend toward electronic interlocks, paralleling developments in automotive safety systems.
Case Study: The Power Bypass Test
One technician, suspecting a dead BICS controller, rigged a direct 12V power and ground wire to the hydraulic lockout solenoid. The lift/tilt functions immediately came alive, confirming the solenoid and valve were mechanically sound. While this bypass disables safety features, it’s a valuable diagnostic tool to isolate electrical faults from hydraulic ones.
Diagnostic Strategy
To troubleshoot hydraulic lockout:

• Inspect BICS panel LEDs for missing or flashing indicators
  
• Check seat switch and lap bar sensor functionality
  
• Locate the BICS solenoid on the main control valve (typically center-mounted)
  
• Test solenoid coil for 12V power using a multimeter
  
• Verify continuity of the dark green wire from controller to solenoid
  
• Examine connector pins for corrosion or loose fit
  
• Consider bypassing the solenoid temporarily to confirm valve operation
  

Best Practices and Cautions

• Never assume controller failure without testing wiring and solenoid
  
• Avoid permanent bypasses that disable safety interlocks
  
• Use dealer diagnostic tools if available—Bobcat’s proprietary BICS tester can confirm controller health
  
• Document wiring changes and restore original configurations after testing
  

Conclusion
Hydraulic lockout on the Bobcat 773 is often a silent failure rooted in electrical interlock systems. By understanding the BICS architecture and methodically testing each component, operators and technicians can restore lift and tilt functionality without guesswork. The evolution from mechanical plungers to electronic solenoids has improved safety but demands a deeper diagnostic approach. With patience and precision, even the most stubborn hydraulic issues can be resolved.