Diagnosing No-Start Conditions in Bobcat Skid Steer Loaders

[MikePhua]

The Bobcat Legacy and Electrical System Overview
Bobcat skid steer loaders have been a cornerstone of compact construction equipment since the 1960s. Known for their maneuverability, hydraulic versatility, and rugged design, Bobcat machines are widely used in landscaping, demolition, agriculture, and snow removal. The company, founded in North Dakota and now part of Doosan Group, has sold hundreds of thousands of units globally, with models ranging from the early 500 series to the modern M2 and R series.
Despite their reliability, Bobcat loaders—especially older models like the 753, 763, and S185—can occasionally suffer from no-start conditions. These issues often stem from electrical faults, fuel delivery problems, or safety interlocks. Understanding the interplay between ignition, starter circuits, and engine sensors is key to resolving such failures.
Terminology Notes

• Solenoid: An electromechanical device that engages the starter motor when the ignition key is turned.
  
• Interlock Circuit: A safety system that prevents engine start unless certain conditions (seat occupied, lap bar down) are met.
  
• Glow Plug: A heating element used to assist cold starts in diesel engines.
  
• ECU (Engine Control Unit): The onboard computer that manages fuel injection, timing, and diagnostics.
  

Common Symptoms of No-Start Conditions
Operators may encounter the following signs when a Bobcat refuses to start:

• No crank when turning the key
  
• Clicking sound from the starter area
  
• Dash lights flicker or fail to illuminate
  
• Glow plug indicator does not activate
  
• Engine cranks but fails to fire
  

In one case, a contractor in Minnesota found his S175 completely unresponsive after a cold night. The issue was traced to a corroded ground strap between the battery and frame, which prevented current flow to the starter solenoid.
Electrical Faults and Diagnostic Steps
Electrical issues are among the most frequent causes of no-start conditions. Begin with:

• Checking battery voltage (should be 12.6V or higher)
  
• Inspecting battery terminals for corrosion or looseness
  
• Verifying ground connections to frame and engine block
  
• Testing the starter solenoid for continuity and engagement
  
• Inspecting fuses and relays in the control panel
  

Use a multimeter to confirm voltage at the ignition switch and starter terminals. If voltage drops significantly during crank attempt, suspect a weak battery or high-resistance connection.
A technician in Ontario resolved a no-start issue by replacing a faulty ignition switch that intermittently failed to send power to the solenoid circuit.
Fuel System and Cold Start Considerations
Diesel Bobcats rely on clean fuel delivery and glow plug operation for reliable starts. Key checks include:

• Ensuring fuel tank is not contaminated or empty
  
• Inspecting fuel filter for clogging or water intrusion
  
• Testing glow plug resistance (typically 0.5–1.5 ohms)
  
• Verifying fuel shutoff solenoid operation
  

In cold climates, fuel gelling can prevent flow to the injectors. Use winter-grade diesel and consider installing a block heater or fuel heater kit.
A farmer in Alberta added a battery-powered glow plug booster to his 763 and eliminated hard starts during −20°C mornings.
Safety Interlocks and Operator Presence Systems
Modern Bobcats include interlock systems that prevent engine start unless:

• The operator is seated
  
• The seat switch is engaged
  
• The lap bar is lowered
  
• The parking brake is set (on some models)
  

If any of these switches fail or become misaligned, the ECU may block starter engagement. Inspect each switch for physical damage, loose wiring, or moisture intrusion.
A rental fleet manager in Georgia discovered that a no-start complaint was due to a seat switch wire pinched under the cushion, causing intermittent contact.
Starter Motor and Engine Mechanical Checks
If electrical and fuel systems check out, consider mechanical issues:

• Starter motor failure due to worn brushes or solenoid
  
• Flywheel teeth damage preventing gear engagement
  
• Engine seizure from lack of oil or internal damage
  

Remove the starter and bench test it with direct battery power. If the motor spins but fails to engage, replace the solenoid or entire unit.
A technician in Colorado found that a Bobcat 753 had a cracked starter housing that misaligned the pinion gear, preventing crank engagement.
Recommendations for Owners and Technicians

• Keep a digital multimeter and jumper leads in the service truck
  
• Clean battery terminals monthly and apply dielectric grease
  
• Replace fuel filters every 250 hours or sooner in dusty conditions
  
• Test glow plugs annually before winter
  
• Document fault codes and symptoms for recurring issues
  

Conclusion
A Bobcat that won’t start can be frustrating, but systematic diagnosis often reveals a straightforward solution. Whether it’s a corroded ground, a faulty interlock switch, or a clogged fuel filter, each component plays a role in the startup sequence. By understanding the electrical, fuel, and safety systems involved, operators and technicians can restore function quickly and keep these versatile machines working through every season and terrain.