What is Liebherr General Fault Code E138?

Fault Code E138 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 either an open circuit, short circuit, or a sensor reading that falls outside the normal operating parameters for the engine's cooling system.

In Liebherr excavators, the coolant temperature sensor plays a critical role in engine management by monitoring coolant temperature and sending this data to the ECM. The ECM uses this information to adjust fuel injection timing, control engine warm-up cycles, and activate cooling fans. When E138 appears, the system cannot reliably monitor engine temperature, potentially leading to overheating, reduced performance, or engine protection mode activation. This is especially critical in used machines where sensor degradation and wiring issues are more common.

Common Symptoms

When fault code E138 is active, operators may experience:

• Check engine light or warning indicator illuminated on the dashboard
• Engine running in derate mode or limited power output to protect components
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Difficulty starting the engine, particularly in cold weather conditions
• Rough idle or irregular engine performance during warm-up phase

Potential Causes

Several factors can trigger E138 in used Liebherr excavators:

• Faulty coolant temperature sensor due to age-related degradation or internal component failure
• Damaged wiring harness or corroded connectors between the sensor and ECM (common rub points near engine mounts)
• Open or short circuit in the sensor signal wire caused by chafing against metal surfaces
• Corroded or loose connector pins at the sensor or ECM connection points
• Low coolant levels causing sensor exposure to air rather than coolant
• ECM software issues or internal ECM faults (less common but possible in older units)

How to Troubleshoot and Fix Code E138

Step 1: Visual Inspection Begin by checking the coolant level in the reservoir and radiator. Inspect the coolant temperature sensor location (typically near the thermostat housing) for physical damage, coolant leaks, or corrosion. On used excavators, pay special attention to wiring harness routing for signs of rubbing, cracking, or heat damage.

Step 2: Electrical Testing Disconnect the sensor connector and use a multimeter to measure resistance across the sensor terminals. Compare readings against Liebherr specifications (typically 2,000-3,000 ohms at 20°C). Check for continuity in the wiring harness from sensor to ECM, and test for shorts to ground. Inspect connector pins for corrosion or bent contacts—common issues in machines with high operating hours.

Step 3: Advanced Diagnostics Connect Liebherr diagnostic software (LiDat) to read live sensor data and compare actual coolant temperature against sensor readings. Monitor voltage signals (typically 0.5-4.5V range) during engine warm-up. If sensor and wiring test within specifications but the code persists, the ECM may require reprogramming or replacement.

Step 4: Component Replacement Replace the coolant temperature sensor with a genuine Liebherr part, applying appropriate thread sealant. Clear fault codes and perform a test run, monitoring for code recurrence.

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Disclaimer: This guide provides general troubleshooting information. Always consult Liebherr service manuals and qualified diesel technicians for complex diagnostics. Improper repairs may cause further damage or safety hazards.