Glow Plug Light Flashing on Bobcat 773

[MikePhua]

Glow Plug System Overview
The glow plug system is a crucial component in diesel engines, designed to heat the combustion chamber to ensure proper ignition, especially in cold conditions. The Bobcat 773 compact track loader, introduced in the late 1990s, utilizes a 3.3-liter three-cylinder Kubota diesel engine. This engine relies on individual glow plugs for each cylinder, controlled by an electronic glow plug relay. The glow plug warning light on the dashboard provides immediate feedback on system status.

Significance of a Flashing Glow Plug Light
A steady glow plug light indicates the engine is preheating properly before starting. A flashing glow plug light, however, signals a fault in the system. Possible causes include:

• Faulty glow plugs or uneven resistance among plugs.
  
• A malfunctioning glow plug relay or control module.
  
• Wiring issues, including corroded connectors or damaged insulation.
  
• Low battery voltage affecting glow plug operation.
  

Flashing light patterns are often designed to indicate specific fault codes, allowing technicians to pinpoint the problem efficiently.

Symptoms and Effects

• Extended cranking time during startup.
  
• Engine misfires or fails to start, particularly in cold weather.
  
• Uneven idle or rough operation immediately after startup.
  

For example, a Bobcat 773 with a weak battery and partially corroded glow plug connectors may display a flashing glow plug light and require multiple attempts to start in subzero temperatures.

Inspection Procedures

• Visual Inspection
  • Check the glow plug wiring harness for damage, corrosion, or loose connections.
    
  • Inspect each glow plug for signs of wear or burn marks.
    
• Resistance Testing
  • Remove glow plugs and measure resistance using a multimeter.
    
  • Typical Kubota 3.3L glow plugs should measure 0.5–1.0 ohms at room temperature. A reading significantly higher or lower indicates a faulty plug.
    
• Relay and Voltage Checks
  • Test the glow plug relay for continuity and correct switching operation.
    
  • Ensure battery voltage remains above 12 volts during glow plug activation; low voltage may cause the system to signal a fault.
    

Repair and Replacement Guidelines

• Replace defective glow plugs individually or as a set if multiple are failing.
  
• Ensure all connectors are clean, tight, and free of corrosion.
  
• If the relay or control module is faulty, replace with an OEM-specified part to maintain proper timing and current control.
  
• Retest the system after repairs to confirm the light now behaves correctly.
  

For preventive maintenance, technicians recommend inspecting the glow plug system every 500–700 engine hours, particularly before winter operation, as cold starts place extra demand on the system.

Case Study
A Bobcat 773 operating on a farm in Arkansas displayed a flashing glow plug light during early morning startup in December. Inspection revealed two glow plugs with resistance readings exceeding 1.5 ohms and one corroded connector at the relay. Replacing the plugs and cleaning the relay connections restored normal operation. After repair, the loader started reliably within three seconds even at -5°C ambient temperature, demonstrating the importance of combining visual inspection with electrical testing.

Preventive Recommendations

• Keep spare glow plugs and connectors on hand for rapid replacement.
  
• Regularly clean battery terminals to maintain sufficient voltage during glow plug operation.
  
• Monitor glow plug light patterns during startup; intermittent flashing may precede full failure.
  
• Document resistance readings of glow plugs during routine service to identify gradual degradation before complete failure.
  

Maintaining the glow plug system ensures consistent engine starts, reduces wear on the starter motor, and prevents downtime during critical operations.