Lift and Dump Failure in the Bobcat 873G and Hydraulic Control Diagnostics

[MikePhua]

The Bobcat 873G and Its Hydraulic Architecture
The Bobcat 873G skid steer loader was introduced in the early 2000s as part of Bobcat’s G-series, designed for high-flow hydraulic applications and heavy-duty lifting. With an operating weight of approximately 7,000 pounds and a rated operating capacity of 2,500 pounds, the 873G is powered by a Deutz diesel engine and features a vertical lift path ideal for loading trucks and handling pallets.
Its hydraulic system is central to its performance, powering lift arms, bucket tilt, auxiliary attachments, and drive motors. The system includes a tandem gear pump, hydraulic control valves, pilot solenoids, and electronic interlocks. When lift and dump functions fail, the issue often lies in the control logic, valve actuation, or safety interlocks—not necessarily in the pump or cylinders themselves.
Terminology Notes

• Lift Circuit: The hydraulic pathway that raises and lowers the loader arms.
  
• Dump Circuit: The hydraulic pathway that tilts the bucket forward or backward.
  
• Interlock System: A safety mechanism that disables hydraulic functions unless specific conditions are met.
  
• Solenoid Valve: An electrically actuated valve that opens or closes hydraulic flow based on control signals.
  

Symptoms of Hydraulic Function Loss
Operators may encounter:

• No response from lift or dump controls
  
• Engine runs normally, drive motors function, but loader arms remain stationary
  
• Audible clicks from solenoids but no hydraulic movement
  
• No fault codes or warning lights on the display
  
• Hydraulic fluid level and filter condition appear normal
  

A contractor in Alberta reported that his 873G suddenly stopped lifting or dumping mid-operation. The drive system remained functional, and the auxiliary hydraulics worked, but the loader arms were frozen.
Initial Diagnostic Strategy
Begin with basic checks:

• Confirm hydraulic fluid level and inspect for contamination
  
• Cycle the seat bar and lap bar to reset interlock system
  
• Test lift and tilt solenoids for voltage during joystick actuation
  
• Inspect fuse panel and relays for blown components
  
• Check for error codes using Bobcat service mode or diagnostic tools
  

A technician in Georgia discovered that the lift solenoid was receiving voltage but not actuating. Replacing the coil restored full function.
Interlock and Safety System Behavior
The Bobcat 873G uses multiple interlocks to prevent unintended movement:

• Seat bar must be down and lap bar engaged
  
• Operator presence switch under the seat must be active
  
• Parking brake must be released
  
• Engine RPM must be above idle threshold
  

If any of these inputs fail, the controller disables hydraulic valve actuation. Recommended steps:

• Test seat switch continuity and replace if intermittent
  
• Inspect lap bar sensor for alignment and wear
  
• Verify parking brake switch output voltage
  
• Use jumper leads to bypass suspected faulty switches during testing
  

A municipal crew in Maine traced a lift failure to a worn seat switch that intermittently lost contact. Replacing the switch resolved the issue and restored lift control.
Valve Block and Solenoid Inspection
If interlocks are confirmed:

• Remove valve block cover and inspect solenoids for corrosion or loose connectors
  
• Test coil resistance (typically 10–20 ohms)
  
• Apply direct 12V power to solenoids to verify actuation
  
• Inspect valve spools for sticking or contamination
  
• Clean valve cavities and replace O-rings if degraded
  

A contractor in Oregon found that the dump valve spool was stuck due to debris from a deteriorated seal. Cleaning the spool and replacing the seal restored bucket tilt.
Electrical and Control System Checks
The 873G relies on analog control signals:

• Inspect joystick wiring harness for abrasion or broken leads
  
• Test control module output voltage to solenoids
  
• Check ground connections at frame and battery
  
• Use a multimeter to verify voltage drop across solenoid terminals
  

A technician in Texas discovered a broken ground strap between the valve block and chassis. Replacing the strap restored full hydraulic function.
Preventive Maintenance and Upgrade Suggestions
To avoid future failures:

• Replace hydraulic filters every 500 hours
  
• Inspect solenoid connectors quarterly
  
• Clean valve block and apply dielectric grease to terminals
  
• Test interlock switches during routine service
  
• Monitor hydraulic fluid temperature and pressure under load
  

Upgrade options:

• Retrofit sealed switches for operator presence and lap bar
  
• Add LED indicators to control panel for solenoid status
  
• Install diagnostic port for quick voltage and pressure testing
  

A contractor in Pennsylvania added a visual indicator for lift and tilt solenoid voltage. This allowed faster troubleshooting and reduced downtime by 40%.
Anecdote from the Field
In 2023, a small excavation firm in Saskatchewan faced repeated lift failures on their Bobcat 873G. The operator suspected a hydraulic pump issue, but a mechanic traced the problem to a faulty lap bar sensor. After replacing the sensor and cleaning the valve block, the machine returned to full operation. The owner later added a laminated wiring diagram to the cab for quick reference.
Conclusion
Lift and dump failures in the Bobcat 873G often stem from interlock logic, solenoid malfunction, or electrical faults—not hydraulic pump failure. With methodical diagnostics and targeted repairs, most issues can be resolved quickly. For operators who rely on precision and uptime, understanding the control system is as important as maintaining the hydraulics. In compact equipment, every switch, wire, and valve plays a role—and every second of downtime matters.