What is Liebherr General Fault Code E151?

Liebherr Fault Code E151 indicates a malfunction in the engine coolant temperature sensor circuit or an implausible coolant temperature reading. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects either an open circuit, short circuit, or out-of-range voltage signal from the coolant temperature sensor (CTS).

In Liebherr excavators, the coolant temperature sensor is critical for engine protection and optimal performance. The ECM relies on accurate temperature data to control fuel injection timing, engine speed limits, and cooling fan operation. When E151 appears, the system typically defaults to a predetermined temperature value, which can lead to inefficient combustion, increased emissions, and potential engine damage if operated under heavy load for extended periods.

Common Symptoms

When fault code E151 is active on your Liebherr excavator, you may experience:

• Engine warning light or malfunction indicator lamp (MIL) illuminated on the dashboard
• Engine operating in derate mode or limp mode, with reduced power output and limited RPM
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Difficult cold starts or rough idling, especially in cooler ambient temperatures
• Abnormal exhaust smoke (black or white) due to improper fuel-air mixture compensation

Potential Causes

The most common technical causes for E151 on used Liebherr excavators include:

• Faulty coolant temperature sensor due to internal resistance drift or element failure (common after 5,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor connector, often caused by vibration or coolant leaks
• Open or short circuit in the sensor signal wire, particularly at known rub points near the engine block mounting brackets
• Corroded or loose ground connections affecting sensor circuit integrity
• Failed ECM (rare, but possible in high-hour machines with moisture exposure)
• Contaminated coolant causing sensor element degradation or buildup on the sensor probe

How to Troubleshoot and Fix Code E151

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor and its wiring harness for obvious damage. Check the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators. Examine the harness routing for wear points where it contacts the engine block or frame.

Step 2: Test Sensor Resistance Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. Compare readings against Liebherr specifications (typically 2,000-3,000 ohms at 20°C/68°F). A reading of infinite resistance indicates an open circuit; near-zero indicates a short.

Step 3: Check Circuit Voltage With the sensor disconnected and ignition on, measure voltage at the ECM side of the harness connector. You should see approximately 5 volts reference voltage. No voltage indicates a wiring issue or ECM problem.

Step 4: Inspect Coolant System Check coolant level and condition. Low coolant can expose the sensor, causing erratic readings. Old, contaminated coolant can coat the sensor element, affecting accuracy.

Step 5: Replace Components If testing confirms sensor failure, replace with a genuine Liebherr or OEM-equivalent coolant temperature sensor. For used machines, also replace the connector pigtail if corrosion is present. After replacement, clear codes using Liebherr diagnostic software and verify proper operation.

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Disclaimer: This guide provides general troubleshooting information for Liebherr fault code E151. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.