T-190 One Side Won’t Move

[MikePhua]

Introduction
The Bobcat T-190 is a compact tracked skid-steer loader commonly used in construction, landscaping, and utility work. It uses a dual hydrostatic drive system—one drive motor for the left track and one for the right—to achieve motion and steering by differential speed control. When one side refuses to move, it can render the machine nearly unusable. Diagnosing this fault requires a systematic look into hydraulics, mechanical linkages, electrical controls, and safety interlocks.
Symptoms and Clues
Operators have reported variations of this problem:

• One track remains stationary while the other still moves.
  
• The affected side behaves as though its parking brake is stuck.
  
• The loader’s lift and bucket functions might be slower or sluggish, suggesting a shared hydraulic issue.
  
• Hydraulic flow or pressure readings are low, pointing toward compromised drive circuit.
  
• LED indicators for traction lock or fault codes may flash, along with audible beeps, when the machine locks up. (E.g., code 06-13 for “no engine speed signal” has been cited)
  

One user recounted that the dealership diagnosed a failed hydro pump plus a bad right drive motor, estimating repair costs in the thousands.
Core System Overview
To understand the failure modes, here’s a simplified breakdown of how the drive works:

• The engine powers a hydraulic pump (or pumps) which provide pressure and flow (charge pressure) to the drive circuits.
  
• Two separate hydrostatic motors (one per track) receive flow from that pump through directional control valves. Speed and direction are dictated by metering via valves tied to the joystick levers.
  
• The parking brake (also called traction lock) is a spring-applied, hydraulically released brake on each side. When hydraulic pressure is applied, it releases the brake; when pressure is lost, the brake engages.
  
• The machine’s control (BICS system in Bobcat parlance) monitors signals such as engine speed, joystick position, and safety switches. If certain fault conditions (e.g. loss of engine speed signal) are detected, the system may disable one or both drive sides for protection.
  

Common Fault Sources
Below are frequent causes for “one side won’t move” symptoms, with explanations and indicators:

• Parking Brake / Traction Lock Solenoid or Valve Failure
   If the solenoid controlling brake release fails (open, shorted, stuck), the side may remain locked even if hydraulic flow is present. Many reports place the parking brake solenoid under the cab, just forward of the pumps, accessible after tilting the cab.
  
• Hydraulic Motor or Drive Motor Failure
   A damaged or failed drive motor may no longer accept flow, appearing locked. Debris or internal wear could cause seizure or internal leakage.
  
• Pump or Charge Pressure Loss
   If the main hydraulic pump is weak, or charge pressure is low (due to belt slippage, worn pump, or internal leakage), there may not be enough pressure to release brakes or drive a motor. One user reported expected aux pressure around 3,300 psi in normal operation.
  
• Faulty Engine Speed Sensor or Signal Disruption
   If the control system loses the engine rpm signal, it may disable hydraulic drive or prevent the parking brakes from releasing to protect the machine. One user had BICS giving code 06-13 (“no engine speed”) and the machine wouldn’t move until that signal was restored.
  
• Sticking or Dirty Control Spools / Valves
   Hydraulic directional control spools or proportional valves can stick or become gummed with debris, leading to incomplete flow or lock-ups.
  
• Electrical or Wiring Faults
   Broken wires, corroded connectors, or shorts in solenoid circuits can interrupt control, causing the system to default into a locked or fault mode.
  

Diagnostic Strategy
Follow these steps to isolate and resolve the issue:

1. Check for Fault Codes
    Watch LED indicators on the BICS panel. If the traction lock LED blinks or specific codes appear (e.g. 06-13), it gives clues to subsystem faults.
   
2. Verify Hydraulic Charge Pressure
    Connect a gauge to appropriate test ports to see if charge (makeup) pressure meets spec. A weak or absent charge pressure suggests pump, belt, or internal leakage issues.
   
3. Isolate Parking Brake Circuit
    Locate the solenoid valve (usually under cab, ahead of pumps). Test continuity, voltage, and actuation. Remove the solenoid and see if manually overriding frees that side.
   
4. Inspect Wiring & Harnesses
    Follow wiring from solenoid, drive motor, and sensor lines. Look for broken insulation, corrosion, or pinched wires, especially near track frame segments where flexing occurs.
   
5. Test the Drive Motor
    If hydraulic flow is present but no rotation occurs, bench test or stall test the motor to determine if it’s internally failed.
   
6. Check Control Spools / Valves
    Remove and clean spool valves in the drive circuit. Sometimes light abrasion and plunger cleaning restore function.
   
7. Inspect Engine Speed Sensor
    Locate the sensor, often installed at the flywheel housing. Test wiring and gap. A failed sensor may disable the traction lock release logic.
   

Real-World Anecdotes
A user replaced the drive motor and hydro pump after dealer diagnosis but complained of high cost and lack of guaranteed operability. This oft-cited example demonstrates how an overlooked simple issue—like a solenoid or electrical fault—can escalate into large repair bills.
Another case involved track replacement preceding the fault, after which the machine’s left side acted as if its parking brake was stuck. One technician suggested the parking brake release circuit couldn’t generate the pressure needed, possibly due to damage while installing the tracks.
Preventive Measures & Best Practices

• Use correct hydraulic fluids, and change them on proper intervals to prevent contaminants from jamming valves.
  
• Avoid repeated directional changes under heavy load; allow pressures to equalize before reversing.
  
• During undercarriage work (track replacement), protect solenoid wiring, hydraulic lines, and avoid bending or pinching.
  
• Keep spare solenoids, sensor units, and O-rings on hand for rapid field repair.
  
• Periodically clean or inspect valves in drive and brake circuits, especially after heavy usage or dusty environments.
  

Conclusion
When a Bobcat T-190 suffers from “one side won’t move,” the root causes typically lie in the parking brake release circuit, hydraulic drive motor, charge pressure, or the machine’s control logic. A systematic diagnostic approach—from fault codes to pressure tests to electrical checks—can efficiently isolate the problem. Though major repairs like motor or pump replacement are expensive, many breakdowns are cured by replacing or repairing solenoids, sensors, or control spools. With prudent maintenance and cautious operation, these faults can be minimized, extending the usefulness of the machine.