Decoding Warning Lights on the Liebherr A 940 Wheeled Excavator

[MikePhua]

Liebherr’s Excavator Legacy and the A 940’s Role
Liebherr, founded in Germany in 1949, has built a reputation for engineering excellence across construction, mining, and material handling. The A 940 wheeled excavator is part of Liebherr’s mid-size mobile excavator lineup, designed for urban infrastructure, roadwork, and utility trenching. With an operating weight around 40,000 pounds and a reach exceeding 30 feet, the A 940 combines hydraulic precision with road mobility.
Unlike tracked excavators, wheeled models like the A 940 offer faster repositioning and reduced surface damage, making them ideal for city environments. The machine’s cab is equipped with a digital display cluster that includes a series of warning and status lights—often referred to informally as “idiot lights”—which alert the operator to system conditions, faults, and maintenance needs.
Terminology Notes

• CAN Bus System: A communication protocol used in modern machinery to link electronic control units and sensors.
  
• ECU (Electronic Control Unit): The onboard computer that monitors and controls engine, hydraulics, and safety systems.
  
• Hydraulic Fault Indicator: A warning light triggered by pressure anomalies or sensor failures in the hydraulic circuit.
  
• Glow Plug Light: A preheat indicator for diesel engines, especially important during cold starts.
  

Understanding the Warning Cluster
The A 940’s dashboard includes a matrix of symbols, each corresponding to a specific system. Common lights include:

• Engine oil pressure
  
• Hydraulic fluid temperature
  
• Brake system fault
  
• Battery voltage warning
  
• Transmission status
  
• Air filter restriction
  
• Diesel particulate filter regeneration
  

These lights are color-coded:

• Red indicates immediate shutdown or critical failure
  
• Yellow signals caution or pending maintenance
  
• Green confirms normal operation or system activation
  

A contractor in Alberta reported that his A 940 displayed a red hydraulic fault light during trenching. After checking fluid levels and inspecting hoses, the issue was traced to a failed pressure sensor near the main valve block. Replacing the sensor cleared the fault and restored full function.
Diagnostic Strategy and Troubleshooting
When a warning light appears:

• Check the operator’s manual for symbol definitions
  
• Use the onboard diagnostic menu to access fault codes
  
• Inspect fluid levels and filter condition
  
• Scan the CAN bus system with a Liebherr-compatible diagnostic tool
  
• Confirm sensor connections and wiring integrity
  

A technician in Georgia diagnosed a persistent brake fault light by tracing the signal wire from the pedal sensor to the ECU. A corroded connector was causing intermittent voltage drop, triggering the warning. Cleaning and resealing the connector resolved the issue.
Common Faults and Their Solutions
Frequent warning light triggers include:

• Low Hydraulic Pressure: Caused by clogged filters, worn pumps, or leaking cylinders. Solution: Replace filters, test pump output, inspect seals.
  
• Engine Overheat: Often due to radiator blockage or coolant loss. Solution: Flush radiator, pressure test cooling system, replace thermostat.
  
• Battery Voltage Drop: May stem from alternator failure or corroded terminals. Solution: Test charging system, clean connections, replace battery if needed.
  
• DPF Regeneration Failure: Diesel particulate filter may not regenerate due to low exhaust temperature. Solution: Perform manual regen cycle, inspect sensors, update ECU software.
  

A municipal crew in Maine experienced repeated DPF faults on their A 940 during winter operations. After installing an exhaust insulation wrap and updating the ECU firmware, the regeneration process stabilized.
Preventive Maintenance and System Monitoring
To reduce warning light occurrences:

• Change engine oil every 250 hours
  
• Replace hydraulic filters every 500 hours
  
• Inspect electrical connectors quarterly
  
• Monitor brake fluid and air pressure weekly
  
• Keep the CAN bus system clean and dry
  

Upgrade options:

• Install a remote diagnostic module for fleet monitoring
  
• Add LED status indicators for better visibility in daylight
  
• Use synthetic hydraulic fluid for better thermal stability
  
• Retrofit vibration dampers to protect sensitive sensors
  

A contractor in Texas added a Bluetooth diagnostic module to his fleet of Liebherr excavators. He now receives fault alerts on his phone and can dispatch technicians with the correct parts before arriving on site.
Anecdote from the Field
In 2023, a small excavation firm in Pennsylvania used an A 940 for sewer line installation. Midway through the job, the glow plug light remained on after startup. The operator suspected a cold-start issue, but diagnostics revealed a faulty temperature sensor feeding incorrect data to the ECU. After replacement, the machine started cleanly and the light cleared. The crew now logs all warning light events and tracks resolution time as part of their maintenance protocol.
Conclusion
Warning lights on the Liebherr A 940 are not just distractions—they are vital indicators of system health and safety. Understanding their meaning, tracing their causes, and responding with precision ensures uptime, protects components, and keeps operators safe. In modern excavators, the dashboard is more than a display—it’s a conversation between machine and operator. Listening carefully makes all the difference.