What is Liebherr General Fault Code E120?

Fault Code E120 indicates a malfunction in the engine coolant temperature sensor circuit or an out-of-range coolant temperature reading. This code is triggered when the Engine Control Module (ECM) detects abnormal voltage signals from the coolant temperature sensor, typically indicating values outside the expected operating range of -40°C to 150°C (-40°F to 302°F).

In Liebherr excavators, the coolant temperature sensor is critical for proper engine management. The ECM uses this data to adjust fuel injection timing, control idle speed, manage the cooling fan operation, and protect the engine from overheating. When E120 appears, the system may default to a predetermined temperature value, which can significantly impact engine performance and fuel efficiency. For used excavators operating in demanding conditions, this fault can lead to reduced productivity and potential engine damage if ignored.

Common Symptoms

• Engine warning light illuminated on the instrument panel, often accompanied by an audible alarm
• Engine running in derate mode (reduced power output) to protect components from potential thermal damage
• Cooling fan running continuously at maximum speed, regardless of actual engine temperature
• Difficulty starting the engine, particularly in cold weather conditions, due to improper fuel mixture calculations
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions

Potential Causes

The most frequent causes of E120 in used Liebherr excavators include:

• Coolant temperature sensor failure due to age, heat cycling, or internal element degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor connector, especially where harnesses route near hot exhaust components or moving parts
• Broken or chafed wires in the sensor circuit caused by vibration or rubbing against frame members (common failure point near engine mounts)
• Corroded or loose ground connections affecting sensor signal integrity
• ECM internal fault (rare, but possible in older machines with 8,000+ hours)
• Coolant contamination causing sensor tip corrosion or coating buildup

How to Troubleshoot and Fix Code E120

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor location (typically on the engine block or cylinder head). Check for physical damage, coolant leaks around the sensor, and corrosion on the connector. On used excavators, pay special attention to harness wear points where cables contact metal surfaces or pass through grommets.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your specific Liebherr service manual for exact specifications). Also check for continuity in the wiring from sensor to ECM and verify proper ground connection with less than 1 ohm resistance.

Step 3: Live Data Analysis Using Liebherr diagnostic software (LiDat or equivalent), monitor live coolant temperature readings while the engine warms up. The temperature should rise gradually and smoothly. Erratic jumps, frozen readings, or values that don't match actual engine temperature indicate sensor or wiring problems.

Step 4: Repair or Replace If testing confirms sensor failure, replace with a genuine Liebherr coolant temperature sensor. For used machines, always apply dielectric grease to connector pins to prevent future corrosion. If wiring damage is found, repair using proper gauge wire and heat-shrink connections, securing cables away from heat sources and moving components.

Disclaimer: This guide provides general troubleshooting information. Always consult your Liebherr service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.