What is Liebherr General Fault Code E109?

Fault Code E109 indicates a malfunction in the engine coolant temperature sensor circuit or an implausible coolant temperature reading. This code is triggered when the Electronic Control Module (ECM) detects a voltage signal from the coolant temperature sensor that falls outside the expected parameters, either too high, too low, or inconsistent with actual operating conditions.

In Liebherr excavators, the coolant temperature sensor plays a critical role in engine management by providing real-time data to the ECM. This information directly influences fuel injection timing, idle speed adjustments, and activation of the cooling fan. When E109 appears, the ECM cannot accurately monitor engine temperature, potentially leading to overheating, poor fuel economy, or engine protection mode activation. For used excavators, this code often signals age-related sensor degradation or wiring issues common in machines with extensive operating hours.

Common Symptoms

• Engine warning light illuminated on the dashboard or operator display panel
• Engine derate mode activated, limiting power output to protect the engine from potential overheating
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Hard starting or rough idle, especially during cold starts when temperature compensation is critical
• Black smoke from the exhaust due to improper fuel mixture adjustments caused by faulty temperature readings

Potential Causes

The most common technical causes for Code E109 in Liebherr excavators include:

• Coolant temperature sensor failure due to internal resistance drift or element degradation (common in machines over 5,000 hours)
• Damaged wiring harness or corroded connectors, particularly at harness rub points near the engine block or frame rails
• Short circuit to ground or open circuit in the sensor signal wire, often caused by vibration damage or rodent activity
• Contaminated coolant causing sensor coating buildup that affects accuracy
• ECM internal fault (rare) where the temperature input circuit has failed
• Poor ground connection at the sensor mounting point due to corrosion or loose hardware

How to Troubleshoot and Fix Code E109

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor and its wiring harness. Check for obvious damage, corrosion on connector pins, or coolant leaks around the sensor. On used excavators, pay special attention to harness routing where it contacts metal edges or moving components—these are common failure points.

Step 2: Resistance Testing Disconnect the sensor and measure its resistance using a digital multimeter. Compare readings against Liebherr specifications (typically 2,000-3,000 ohms at 20°C). Test at different temperatures if possible; resistance should decrease smoothly as temperature increases. Erratic readings indicate sensor replacement is needed.

Step 3: Circuit Verification With the sensor disconnected, check for continuity in the signal wire back to the ECM and verify proper ground connection. Measure voltage supply from the ECM (usually 5V reference). Check for shorts to ground or power using resistance measurements with all connectors separated.

Step 4: Connector and Coolant Inspection Clean all connector terminals with electrical contact cleaner and apply dielectric grease. Verify coolant condition—contaminated or old coolant can coat sensors. For used machines, consider replacing the sensor preemptively if it's original equipment with over 6,000 operating hours.

Step 5: Clear Code and Test After repairs, clear the fault code using Liebherr diagnostic software (LiDat) or compatible scan tool. Run the engine through temperature cycles while monitoring live data to confirm proper sensor operation and verify the code doesn't return.

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Disclaimer: This guide provides general troubleshooting information. Always consult Liebherr service manuals and qualified diesel technicians for your specific machine model. Improper diagnostics can lead to further damage or safety hazards.