Diagnosing Low Hydrostatic Pressure Faults on Bobcat T190 Loaders

[MikePhua]

The Bobcat T190 and Its Hydraulic Architecture
The Bobcat T190 compact track loader was introduced in the early 2000s as part of Bobcat’s push into mid-size tracked machines. With a rated operating capacity of 1,900 lbs and a vertical lift path, the T190 became popular for grading, material handling, and site prep. Powered by a 66 HP Kubota diesel engine and equipped with a hydrostatic drive system, the T190 uses dual hydraulic pumps to power both propulsion and auxiliary functions.
Bobcat, founded in 1947 and now part of the Doosan Group, has sold hundreds of thousands of compact loaders globally. The T190 remains a workhorse in rental fleets and contractor yards, though aging units often present diagnostic challenges due to wear and limited onboard diagnostics.
Terminology Annotation

• Hydrostatic Drive: A propulsion system using hydraulic fluid to transmit power from the engine to the drive motors.
  
• Charge Pressure: The baseline hydraulic pressure that feeds the hydrostatic pumps, typically maintained by a charge pump.
  
• Fault Code 05-09 / 05-14 / 05-15: Diagnostic codes indicating low or extremely low hydrostatic charge pressure, often triggering engine shutdown.
  

Symptoms and Initial Observations
Operators encountering fault codes 05-09, 05-14, or 05-15 on a Bobcat T190 often report:

• Engine shutdown at idle (around 1150 RPM)
  
• Normal operation at higher RPMs (above 1300)
  
• Non-functional brake and traction lock systems
  
• Dash panel showing low pressure readings (e.g., 50 psi at idle)
  

These symptoms suggest that the hydrostatic charge pressure is falling below safe operating thresholds, causing the machine to enter a protective shutdown mode. The brake system, which relies on hydraulic pressure to release, also fails when charge pressure drops.
Common Causes and Diagnostic Pathways
Several potential causes can trigger low charge pressure faults:

• Worn or failed charge pump within the hydrostatic unit
  
• Broken or slipping drive belt between engine and pump
  
• Clogged hydraulic filters or suction screens
  
• Electrical faults in pressure sensors or wiring harness
  
• Incorrect fluid viscosity or contamination
  

In one case, a technician discovered that the main drive belt had snapped, leaving the pumps unpowered despite the engine running normally. Another operator found that the charge pressure at idle was only 50 psi, far below the expected 350–400 psi range.
Terminology Annotation

• Drive Belt: A rubber belt that transmits rotational power from the engine to the hydraulic pumps.
  
• Deluxe Panel: An advanced dashboard interface on Bobcat machines that displays real-time system pressures and fault codes.
  

Sensor Accuracy and Mechanical Verification
While the dash panel provides pressure readings, these can be misleading if the sensor itself is faulty. To confirm actual charge pressure:

• Connect a mechanical gauge to the charge pressure test port
  
• Compare readings at idle and full throttle
  
• Inspect sensor wiring for corrosion or damage
  
• Replace suspect sensors and retest
  

A mechanic in Maine emphasized that relying solely on digital readings can lead to misdiagnosis. In his experience, a faulty sensor once reported 50 psi when actual pressure was over 300 psi.
Brake and Traction Lock Behavior
The Bobcat T190 uses hydraulic pressure to release the spring-applied brakes. When charge pressure drops, the brakes engage automatically. If the brake wire only shows 5 volts instead of the expected 12, it may indicate a voltage drop due to poor grounding or a failing relay.
To troubleshoot:

• Check voltage at the brake solenoid
  
• Inspect relays and fuses in the control panel
  
• Verify traction lock override switch functionality
  
• Test continuity across the brake circuit
  

Recommendations for Field Technicians
To resolve low hydrostatic pressure faults:

• Inspect and replace drive belt if worn or broken
  
• Replace hydraulic filters and flush fluid if contaminated
  
• Test charge pressure with a mechanical gauge
  
• Verify sensor accuracy and replace if needed
  
• Check brake and traction lock circuits for voltage and continuity
  
• Use Bobcat diagnostic software if available to access deeper fault logs
  

Preventive measures include:

• Changing hydraulic fluid every 500 hours
  
• Replacing filters every 250 hours
  
• Inspecting drive belt tension monthly
  
• Monitoring fault codes and pressure readings during startup
  

Conclusion
Low hydrostatic pressure faults on the Bobcat T190 can stem from mechanical, hydraulic, or electrical issues. Accurate diagnosis requires both sensor verification and physical inspection. With proper maintenance and systematic troubleshooting, technicians can restore full functionality and prevent costly downtime. Whether grading a driveway or loading debris, the T190 depends on stable charge pressure to keep moving—and stopping—safely.