Resolving Code 79-10 on the Bobcat T250 Skid Steer Loader

[MikePhua]

The Bobcat T250 and Its Diagnostic System
The Bobcat T250 is a mid-sized tracked skid steer loader introduced in the early 2000s by Bobcat Company, a division of Doosan Group. Designed for high lift capacity and stability, the T250 features a vertical lift path, hydrostatic drive, and a 75-horsepower turbocharged diesel engine. It was widely adopted in construction, landscaping, and rental fleets due to its balance of power and maneuverability.
The T250 is equipped with an onboard diagnostic system that displays fault codes on the instrument panel. These codes are intended to help operators and technicians identify issues related to engine, hydraulics, electrical systems, and safety interlocks. However, not all codes are documented in the operator’s manual, and some—like 79-10—may be considered “false codes,” meaning they do not correspond to a specific fault but instead indicate a systemic or communication error.
Terminology and Component Notes
- Fault Code: A numeric identifier displayed on the machine’s panel indicating a system error or warning.
- False Code: A diagnostic code that appears without a corresponding fault in the manual or system logic.
- Interlock System: A safety feature that prevents machine movement unless certain conditions are met (e.g., seat occupied, lap bar down).
- ECU (Electronic Control Unit): The onboard computer that manages engine and hydraulic functions.
- CAN Bus: A communication protocol used to transmit data between electronic modules.
Symptoms and Initial Observations
In one reported case, a Bobcat T250 displayed fault code 79-10 and became unresponsive. The engine would start, but none of the hydraulic or drive functions would engage. The operator contacted the manufacturer and was informed that the code was not listed in the manual and was likely a false code. This suggests a communication breakdown or a misinterpreted signal within the control system.
Common symptoms include:

• Engine starts normally but no movement or hydraulic response
  
• Fault code 79-10 appears immediately after startup
  
• No other warning lights or audible alarms
  
• Safety interlocks appear to be engaged correctly
  

Diagnostic Strategy and Troubleshooting Steps
To resolve the issue, technicians should begin by verifying the integrity of the interlock system and electrical connections. False codes often stem from poor grounding, voltage fluctuations, or CAN bus interference.
Recommended steps:

• Inspect all ground straps and battery terminals for corrosion or looseness
  
• Check voltage at the ECU during startup to ensure stable power delivery
  
• Verify that the seat switch, lap bar sensor, and auxiliary hydraulics are functioning
  
• Disconnect and reconnect the main harness to reset communication
  
• Use a Bobcat diagnostic tool to scan for hidden or secondary codes
  

If the code persists after these checks, the issue may lie in the ECU firmware or a failing sensor that intermittently disrupts communication.
Field Anecdotes and Practical Solutions
One technician shared that a similar issue on a T300 was resolved by replacing the seat switch, which had degraded internally and sent erratic signals to the ECU. Although the switch passed a basic continuity test, its resistance fluctuated under load, triggering false interlock faults.
Another operator found that a weak battery caused intermittent voltage drops during startup, confusing the ECU and triggering false codes. After replacing the battery and cleaning the terminals, the machine returned to normal operation.
Preventative Maintenance and Long-Term Reliability
To prevent recurrence of false codes:

• Replace batteries every 3–4 years or when voltage drops below 12.4V under load
  
• Inspect and clean all electrical connectors quarterly
  
• Use dielectric grease on exposed terminals to prevent corrosion
  
• Avoid jump-starting with high-amperage sources that may spike voltage
  
• Keep the diagnostic port clean and covered to prevent moisture intrusion
  

For machines operating in wet or dusty environments, consider installing sealed connectors and routing harnesses through protective conduit.
Bobcat Company and Diagnostic Philosophy
Bobcat, founded in 1947 in North Dakota, has long emphasized operator safety and machine intelligence. The T250 was part of a generation that introduced more advanced diagnostics and electronic control systems. While these systems improve performance and safety, they also require disciplined maintenance and familiarity with electronic troubleshooting.
Bobcat’s diagnostic codes are designed to be intuitive, but undocumented codes like 79-10 highlight the need for updated manuals and technician training. As machines become more software-driven, false codes may become more common—making field experience and communication with manufacturers essential.
Conclusion
Code 79-10 on the Bobcat T250 is a reminder that not all faults are mechanical. Electrical noise, sensor degradation, and communication glitches can paralyze a machine without leaving a clear trail. By methodically inspecting the interlock system, power supply, and ECU signals, technicians can restore functionality and prevent future disruptions. In modern equipment, the brain is just as important as the brawn—and sometimes, a ghost in the wire is the real culprit.