Why Does the Air Filter Restriction Light Stay On in a Bobcat S250

[MikePhua]

The Bobcat S250 and Its Air Intake System
The Bobcat S250 skid steer loader was introduced in the early 2000s as part of Bobcat’s high-performance 200 series. With a rated operating capacity of 2,500 lbs and a turbocharged diesel engine producing around 75 hp, the S250 became a favorite among contractors for its power-to-size ratio and hydraulic versatility. Bobcat, founded in 1947, has sold hundreds of thousands of skid steers globally, and the S250 remains a common sight on job sites and rental fleets.
The air intake system on the S250 includes a dual-stage filtration setup: an outer primary filter and an inner safety filter. These components are housed in a cylindrical canister mounted near the engine compartment. A restriction sensor monitors airflow and triggers a dashboard warning light when pressure drops below a set threshold—typically due to clogging or filter degradation.
Terminology Notes

• Primary Filter: The outer element that traps larger dust and debris particles.
  
• Safety Filter: The inner element that captures fine particles and protects the engine during primary filter failure.
  
• Restriction Sensor: A vacuum-sensitive switch that detects reduced airflow and activates a warning light.
  
• Micro-Screen Filter: A non-washable filter made of fine mesh or synthetic media, often used as a safety element.
  

Symptoms and Initial Observations
In one case, the air filter restriction light remained on despite the primary filter being relatively clean and only 150 hours old. The operator blew out the filter and even ran the machine with only the inner filter installed, but the warning persisted. This raised questions about how the system detects restriction and whether the filters were functioning correctly.
Key observations included:

• The inner filter was green, while replacements were white—suggesting a possible material or design change.
  
• The inner filter appeared clean but was not replaced.
  
• The restriction light stayed on regardless of filter configuration.
  

Sensor Behavior and Filter Compatibility
The restriction sensor operates by detecting vacuum pressure in the intake system. If airflow is impeded—either by clogged filters or collapsed media—the sensor triggers the warning light. However, even a clean-looking filter can cause restriction if:

• The media is degraded or collapsed internally
  
• The filter is not OEM or lacks proper airflow rating
  
• The safety filter is partially blocked or incompatible
  

Green-colored filters may indicate aftermarket or washable variants, but most micro-screen safety filters are not washable. Attempting to clean them can damage the media and reduce airflow, triggering false restriction alerts.
Operator Anecdotes and Practical Advice
One technician in the Philippines shared that a JCB engine rebuild was prompted by a persistent restriction light—only to discover the inner filter was the culprit. After replacing it with a factory-specified unit, the issue resolved. Another operator in Alaska noted that his S250 ran fine but the light stayed on until both filters were replaced with OEM parts.
A mechanic in Montana emphasized that aftermarket filters often have different flow characteristics. He recommended using Bobcat-branded filters or verified equivalents and replacing both elements together.
Preventive Measures and Recommendations

• Replace Both Filters Together: Even if the safety filter looks clean, it may be restricting flow.
  
• Use OEM or Verified Filters: Ensure proper airflow rating and compatibility.
  
• Inspect Sensor Wiring: A damaged wire or connector can cause false alerts.
  
• Avoid Washing Safety Filters: Micro-screen elements are not designed for reuse.
  
• Reset the Sensor After Service: Some models require manual reset or cycling to clear the warning.
  

Conclusion
A persistent air filter restriction light on a Bobcat S250 often points to a degraded or incompatible safety filter—even when the primary filter appears clean. By replacing both filters with OEM-rated components and inspecting the sensor system, operators can restore proper airflow and eliminate false warnings. The S250’s robust engine depends on clean, unrestricted air—and its sensor system is only as reliable as the filters it monitors.