Troubleshooting the Shutoff Solenoid in a Bobcat 773G

[MikePhua]

The Bobcat 773G and Its Role in Compact Equipment Evolution
The Bobcat 773G skid steer loader is part of the G-series lineup that helped redefine compact equipment in the late 1990s and early 2000s. Manufactured by Bobcat Company, a pioneer in the compact equipment industry since its founding in 1947, the 773G was designed for versatility, durability, and ease of maintenance. With a rated operating capacity of approximately 1,750 lbs and a turbocharged diesel engine producing around 46 horsepower, the 773G became a popular choice for contractors, landscapers, and municipal fleets.
Bobcat’s reputation for innovation stems from its development of the first compact loader in 1958. By the time the 773G was introduced, the company had already sold hundreds of thousands of machines globally. The G-series incorporated improved operator comfort, better hydraulic performance, and enhanced electrical systems—though these systems occasionally presented challenges, particularly in components like the shutoff solenoid.
Understanding the Shutoff Solenoid System
The shutoff solenoid in the Bobcat 773G is a critical component of the fuel delivery system. It controls the flow of diesel to the engine by retracting or extending a plunger that engages the fuel lever. When the ignition is turned on, the solenoid receives signals from the Electronic Control Unit (ECU) to energize and allow fuel flow. When the key is turned off, the solenoid deactivates, cutting fuel and stopping the engine.

• Pull Wire (Red, Wire 8100): Receives battery voltage via the fuel relay for a brief moment during startup to retract the plunger.
  
• Hold Wire (White, Wire 8800): Receives continuous voltage directly from the ECU to keep the plunger retracted while the engine runs.
  
• Ground Wire (Black): Provides the return path for electrical current.
  

Terminology Annotation

• ECU (Electronic Control Unit): The onboard computer that manages engine functions, including fuel delivery and diagnostics.
  
• Fuel Relay: An electromechanical switch that controls high-current flow to the solenoid based on ECU signals.
  
• Ohm Test: A diagnostic method using a multimeter to measure electrical resistance across solenoid coils.
  

Common Issues and Diagnostic Steps
One recurring issue with the 773G involves trouble code 13-07, which typically indicates a fault in the fuel solenoid circuit. Operators may experience a no-start condition, even after replacing the solenoid. In such cases, the problem often lies in the wiring, relay, or ECU signal integrity.
Recommended diagnostic steps include:

• Verify battery voltage at relay terminal #30
  
• Confirm ground at terminal #85
  
• Check for transient ground signal at terminal #87 during key-on
  
• Perform ohm test on solenoid:
  • Red to black: ~10.9 ohms
    
  • White to black: ~0.26 ohms
    
• Back-probe ECU connectors to confirm signal continuity
  

If all wiring checks out and the solenoid tests within spec, the issue may reside in the ECU itself. Unfortunately, the 773G’s ECU stores fault codes that cannot be manually cleared without dealer software. This has led some operators to bypass the system entirely.
Field Modifications and Workarounds
In one case, a technician acquired a 773G missing its solenoid entirely. The previous owner had rigged a spring to hold the fuel lever open and wired the starter directly to a pushbutton switch. While this allowed the machine to run, it disabled safety interlocks and diagnostic capabilities.
After extensive troubleshooting, the technician installed a new solenoid and verified all wiring. However, the machine still refused to start due to the persistent fault code. Without access to dealer software, he wired a manual switch to energize the solenoid and retained the pushbutton starter. Though not ideal, this workaround restored functionality and allowed the machine to operate safely under supervision.
Industry Trends and ECU Diagnostics
Modern skid steers increasingly rely on integrated diagnostics and encrypted ECUs. Manufacturers like Bobcat, John Deere, and Case have adopted proprietary software tools that limit third-party access. This trend has sparked debate in the equipment community, with calls for more open-source diagnostic standards.
In 2023, a bill was introduced in the U.S. Congress advocating for “Right to Repair” legislation in the heavy equipment sector. If passed, it would require manufacturers to provide access to diagnostic tools and software for independent technicians. The Bobcat 773G, while older, remains a symbol of this transition period—where mechanical reliability meets electronic complexity.
Preventive Measures and Long-Term Solutions
To avoid solenoid-related issues in the 773G:

• Inspect wiring harnesses for corrosion or abrasion
  
• Replace relays with OEM-grade components
  
• Use dielectric grease on connectors to prevent moisture ingress
  
• Schedule ECU scans annually if operating in critical environments
  
• Avoid bypassing safety systems unless absolutely necessary
  

For long-term reliability, consider upgrading to newer Bobcat models with improved diagnostic access and modular electronics. However, for owners committed to maintaining their 773G, investing in a service manual and building relationships with local dealers remains essential.
Conclusion
The shutoff solenoid in the Bobcat 773G is more than a simple actuator—it’s a gateway to understanding the machine’s electrical architecture. While troubleshooting can be complex, especially with ECU-stored fault codes, a methodical approach rooted in electrical fundamentals can restore functionality. As compact equipment continues to evolve, the lessons learned from machines like the 773G remain invaluable for technicians, operators, and equipment historians alike.