Solving EGR Faults on the Bobcat S650

[MikePhua]

The Bobcat S650 and Its Emissions System
The Bobcat S650 skid steer loader was introduced in the early 2010s as part of Bobcat’s M-Series, designed to meet Tier 4 emissions regulations while delivering high breakout force and hydraulic performance. Powered by a turbocharged Doosan diesel engine, the S650 produces around 74 horsepower and features a vertical lift path ideal for loading and material handling. Bobcat, founded in 1947 and headquartered in North Dakota, has sold millions of compact machines globally, with the S650 becoming one of its most popular models in North America and Europe.
To comply with emissions standards, the S650 uses an Exhaust Gas Recirculation (EGR) system. This system redirects a portion of exhaust gases back into the combustion chamber to reduce nitrogen oxide (NOx) emissions. While effective, EGR systems are prone to carbon buildup, sensor faults, and valve failures—especially in cold climates or under heavy load.
Common EGR Fault Codes and Their Meaning
When the S650 displays EGR-related fault codes, it typically signals one of the following issues:

• EGR valve stuck open or closed: Causes poor combustion and reduced power.
  
• EGR temperature sensor fault: Leads to incorrect exhaust flow regulation.
  
• EGR position sensor error: Prevents accurate valve movement tracking.
  
• Excessive soot buildup: Restricts flow and triggers fault codes.
  
• Low voltage or wiring issues: Disrupts sensor communication.
  

Operators often report reduced engine power, erratic idle, and warning lights when these faults occur. In cold weather, the problem may be exacerbated by moisture condensation and soot accumulation.
Locating and Inspecting the EGR Valve
On the Doosan engine used in the S650, the EGR valve is typically mounted near the front of the engine, close to the hydrostatic pump side. Accessing it requires removing the engine cover and possibly the air intake ducting.
Inspection steps:

• Check for visible carbon buildup around the valve housing
  
• Remove the valve and inspect the pintle for sticking or scoring
  
• Clean the valve using EGR-safe solvent and a soft brush
  
• Test valve movement manually or with diagnostic software
  
• Inspect wiring harness and connectors for corrosion or damage
  

In one case from Minnesota, a contractor found that his EGR valve was completely plugged after a week of sub-zero operation. After cleaning the valve and resetting the fault code, the machine returned to full power.
Sensor Diagnostics and Electrical Checks
The EGR system relies on multiple sensors to monitor temperature, valve position, and flow rate. Faulty sensors can mimic mechanical failure or trigger limp mode.
Recommended checks:

• Use a multimeter to verify voltage at each sensor
  
• Compare resistance values to manufacturer specifications
  
• Inspect connectors for bent pins or moisture intrusion
  
• Replace sensors showing erratic readings or physical damage
  

A technician in Alberta once traced an intermittent EGR fault to a cracked sensor housing that allowed water ingress. After replacing the sensor and sealing the connector with dielectric grease, the issue was resolved.
Resetting Fault Codes and Restoring Performance
After cleaning or replacing EGR components, fault codes must be cleared to restore full engine performance. This can be done using Bobcat’s diagnostic software or a compatible scan tool.
Steps:

• Connect diagnostic tool to machine’s service port
  
• Access emissions system menu
  
• Clear active fault codes
  
• Perform system test to verify valve movement and sensor response
  
• Monitor engine performance during warm-up and under load
  

In some cases, the fault code may clear itself after several successful cycles. However, persistent codes require manual reset to exit limp mode.
Preventive Maintenance and Cold Weather Strategies
To reduce EGR faults and extend system life:

• Clean EGR valve every 500 hours or annually
  
• Use ultra-low sulfur diesel to minimize soot
  
• Avoid idling for long periods in cold weather
  
• Install engine block heaters in sub-zero climates
  
• Inspect sensors and wiring during routine service
  

Operators in northern regions often pre-warm their machines before operation. In Alaska, a fleet manager reported that using heated garages and block heaters reduced EGR faults by 70% during winter months.
Field Stories and Operator Ingenuity
In Wisconsin, a landscaper noticed his S650 losing power during snow removal. The fault code pointed to EGR valve failure. After removing the valve, he discovered a thick layer of soot and ice. He cleaned the valve, installed a preheater, and added a fuel additive to reduce carbon formation. The machine ran clean for the rest of the season.
In another case from Germany, a technician retrofitted a transparent EGR hose to monitor flow visually. This helped him detect partial blockages before fault codes appeared, improving uptime and reducing diagnostic time.
Conclusion
EGR fault codes on the Bobcat S650 are not just technical annoyances—they’re indicators of emissions system stress that can impact performance and compliance. By understanding the system’s components, performing targeted diagnostics, and adopting preventive strategies, operators can keep their machines running smoothly and within regulatory limits. Whether clearing snow in Minnesota or grading soil in Bavaria, the S650’s EGR system demands attention, but rewards diligence with reliable power and cleaner operation.