Resolving Flashing Indicator Lights on the Bobcat 853 BICS System

[MikePhua]

The Bobcat 853 and Its Control Architecture
The Bobcat 853 skid steer loader was introduced in the early 1990s as part of Bobcat’s 800-series lineup, designed for mid-range construction, landscaping, and agricultural tasks. Powered by a 58-horsepower Kubota diesel engine, the 853 featured hydrostatic drive, auxiliary hydraulics, and the Bobcat Interlock Control System (BICS)—a safety innovation that electronically monitors operator presence and system readiness.
BICS was developed to prevent unintended movement of the loader arms and drive system unless specific conditions were met. These include seat occupancy, seat bar engagement, and proper voltage levels. The system uses sensors, relays, and indicator lights to communicate status to the operator.
Terminology annotation:
- BICS (Bobcat Interlock Control System): An electronic safety system that disables loader and drive functions unless operator presence and safety conditions are confirmed.
- Overvoltage/undervoltage fault: A condition where the system detects electrical supply outside the safe operating range, triggering a shutdown or warning.
- Indicator lights: Dashboard LEDs that signal system status, faults, or readiness.
- Seat bar switch: A sensor that detects whether the safety bar is lowered across the operator’s lap.
Symptoms of System Fault and Diagnostic Clues
In one reported case, all BICS indicator lights on a Bobcat 853 began flashing simultaneously. According to the service manual, this behavior typically indicates either an overvoltage or undervoltage condition. The machine may still crank and run, but hydraulic and drive functions remain disabled until the fault is cleared.
This issue often arises from:

• Weak battery or poor charging
  
• Corroded ground connections
  
• Faulty alternator output
  
• Loose or damaged wiring harness
  
• Sensor failure or misalignment
  

Voltage irregularities confuse the BICS logic, causing it to enter a fault state. The system is designed to protect against erratic behavior caused by unstable power supply.
Recommended Diagnostic Procedure
To isolate the fault:

• Measure battery voltage with engine off (should be 12.6–12.8V)
  
• Measure voltage with engine running (should be 13.8–14.5V)
  
• Inspect battery terminals for corrosion or looseness
  
• Check ground strap from battery to frame and engine block
  
• Verify alternator output and belt tension
  
• Inspect wiring harness for chafing, pinched wires, or loose connectors
  
• Test seat bar and seat switch continuity
  

If voltage readings are outside the expected range, replace the battery or alternator as needed. A weak battery may pass a static test but fail under load, especially during cold starts.
Resetting the BICS System and Clearing Faults
Once the voltage issue is resolved, the BICS system may reset automatically. If not, perform the following:

• Turn off ignition and remove key
  
• Disconnect battery for 5 minutes
  
• Reconnect battery and turn ignition on
  
• Lower seat bar and sit in seat
  
• Observe indicator lights for normal sequence
  

If lights continue flashing, inspect the BICS module itself. Some units may require manual reset or replacement if internal components are damaged.
Field Anecdote and Operator Insight
One operator in Wisconsin encountered flashing lights after replacing a weak battery. Despite installing a new unit, the fault persisted. Upon closer inspection, he found the ground strap corroded beneath the paint at the frame connection. After cleaning the contact point and reinstalling the strap with dielectric grease, the system reset and operated normally.
This highlights the importance of not just replacing parts, but verifying the integrity of electrical paths. Ground faults are a common but overlooked cause of electronic malfunctions in older equipment.
Preventive Measures and Long-Term Reliability
To maintain BICS functionality:

• Inspect electrical connections quarterly
  
• Use sealed batteries with proper cold cranking amps
  
• Apply dielectric grease to connectors and grounds
  
• Avoid jump-starting with high-output chargers
  
• Keep wiring harnesses secured and away from moving parts
  

For machines stored outdoors or used in wet conditions, consider adding a battery disconnect switch to prevent parasitic drain and corrosion.
Conclusion
Flashing lights on the Bobcat 853’s BICS system are more than a nuisance—they’re a signal of electrical instability that can disable critical functions. By methodically checking voltage levels, inspecting grounds, and understanding the system’s logic, operators can restore functionality and avoid unnecessary downtime. In a machine built for hard work, even the smallest wire can make the biggest difference.