Troubleshooting Lift Arm Failure on the Bobcat S175

[MikePhua]

Lift Arm Malfunction Often Traces Back to Hydraulic Flow or Control Logic
When a Bobcat S175 skid-steer loader experiences lift arm failure—especially when the arms rise only partially or not at all—the issue typically stems from hydraulic flow restriction, control valve blockage, or auxiliary circuit interference. The S175, introduced in the early 2000s, is a mid-frame loader powered by a 49 hp Kubota diesel engine and equipped with either foot pedals or joystick controls depending on configuration. Its hydraulic system is capable of delivering up to 16.9 gallons per minute at 3,300 psi, sufficient for lifting over 1,750 lbs.
Joystick-Controlled Machines Require Electronic and Hydraulic Coordination
In joystick-controlled variants, the lift function is governed by an electro-hydraulic valve block beneath the operator seat. Signals from the joystick trigger solenoids that direct flow to the lift cylinders. If the arms rise only 50 cm and stall, as reported in some cases, the system may be suffering from:

• Restricted flow due to a clogged valve port or muffled orifice
  
• Auxiliary hydraulic circuit stuck in open or deadhead mode
  
• Low system pressure caused by belt slippage or pump inefficiency
  
• Faulty solenoid or spool lock preventing valve actuation
  

One operator noted that the lift arms only responded when the bucket curl function was engaged simultaneously, suggesting that flow was being redirected or boosted through shared circuits. This behavior points to a possible auxiliary circuit override, where deadheading an attachment causes pressure anomalies in the main lift circuit.
Drive Belt and Tensioner Issues Can Affect Hydraulic Output
The Bobcat S175 uses a serpentine belt to drive the hydraulic pump. If the belt tensioner bearing fails or loosens repeatedly, pump speed may drop, reducing pressure and flow. While complete belt failure would disable all hydraulic functions, partial slippage can selectively impair high-demand operations like lifting.
To verify belt integrity:

• Inspect the tensioner pulley for bearing play or misalignment
  
• Check belt tension with a calibrated gauge
  
• Replace worn belts with OEM-rated components
  
• Monitor pump RPM under load using diagnostic software or tachometer
  

Auxiliary Circuit Interference and Relief Valve Behavior
When attachments like grapples or hydraulic hammers are used without proper relief valves, pressure can backfeed into the lift circuit. Genie and Bobcat recommend installing port relief valves on auxiliary lines to prevent system imbalance. Without these, the lift arms may raise but fail to lower, or tilt functions may become unresponsive.
To isolate the issue:

• Disconnect the auxiliary attachment and test lift independently
  
• Inspect the auxiliary solenoid for stuck spool or electrical fault
  
• Check for pressure buildup in the return line using a gauge
  

No Fault Codes Does Not Mean No Faults
Even if the machine displays no error codes, mechanical or hydraulic faults may still exist. The Bobcat S175’s onboard diagnostics only monitor electrical signals and sensor feedback. Manual testing of pressure, flow, and valve response is essential.
Recommendations for Restoration

• Flush the hydraulic system and replace filters
  
• Clean or replace the lift control valve block
  
• Inspect joystick wiring and solenoid connectors
  
• Install auxiliary relief valves if using high-flow attachments
  
• Replace belt tensioner and verify pump output
  

Conclusion
Lift arm failure on the Bobcat S175 is often a multi-layered issue involving hydraulic flow, control valve logic, and auxiliary circuit behavior. By methodically testing each subsystem and addressing wear components like belts and solenoids, operators can restore full lift function and prevent future downtime. The S175 remains a reliable workhorse when maintained with attention to hydraulic integrity and control calibration.