What is Liebherr General Fault Code E122?

Fault Code E122 indicates a malfunction in the engine coolant temperature sensor circuit or an implausible coolant temperature reading detected by the Electronic Control Module (ECM). This code is triggered when the ECM receives voltage signals outside the expected range from the coolant temperature sensor (CTS), or when the sensor reading doesn't correlate with engine operating conditions.

In Liebherr excavators, the coolant temperature sensor plays a critical role in engine management. The ECM relies on accurate temperature data to optimize fuel injection timing, control engine warm-up enrichment, manage cooling fan operation, and protect the engine from overheating. When E122 appears, the system may enter a default mode using substitute values, which can significantly impact machine performance, fuel efficiency, and potentially lead to engine damage if the actual coolant temperature is dangerously high.

Common Symptoms

• Warning light or alarm illuminated on the instrument cluster, often accompanied by a temperature-related icon
• Reduced engine power (derate mode) as the ECM implements protective measures based on assumed temperature values
• Cooling fan running continuously at maximum speed, regardless of actual engine temperature
• Difficulty starting or rough idle, especially during cold starts when the ECM cannot properly adjust fuel delivery
• Erratic temperature gauge readings that fluctuate abnormally or remain fixed at one extreme

Potential Causes

The most common technical causes for E122 in used Liebherr excavators include:

• Faulty coolant temperature sensor due to internal element degradation (particularly common after 5,000+ operating hours)
• Damaged or corroded wiring harness at the sensor connector, especially where the harness routes near hot engine components or sharp edges
• Broken or shorted wiring between the sensor and ECM, often caused by vibration-induced wire chafing at mounting points
• Corroded or loose connector pins at either the sensor or ECM connection points—moisture intrusion is common in older machines
• Low coolant level causing air pockets near the sensor, resulting in inaccurate readings
• ECM internal fault (less common) affecting the temperature input circuit

How to Troubleshoot and Fix Code E122

Step 1: Visual Inspection and Preliminary Checks Begin by inspecting the coolant level in the radiator and expansion tank. Low coolant can cause false readings. Next, locate the coolant temperature sensor (typically mounted on the engine block or cylinder head near the thermostat housing). Carefully examine the sensor connector for corrosion, moisture, or damaged pins. On used excavators, pay special attention to wire harness routing—look for evidence of rubbing against brackets, heat damage from exhaust components, or cracking in the insulation.

Step 2: Electrical Testing with Diagnostic Tools Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures. A typical CTS should show approximately 2,000-3,000 ohms at room temperature, decreasing to 200-300 ohms when hot (refer to Liebherr specifications for exact values). Test the wiring harness continuity from the sensor connector back to the ECM using a wiring diagram. Check for proper voltage supply (typically 5V reference voltage) at the sensor connector with the ignition on and sensor disconnected.

Step 3: Component Replacement and System Verification If the sensor readings are out of specification, replace the coolant temperature sensor with a genuine Liebherr or OEM-equivalent part. Before installation, apply dielectric grease to connector pins to prevent future corrosion—critical for used machines operating in harsh environments. If wiring damage is found, repair or replace the affected harness section with proper strain relief. After repairs, clear the fault code using Liebherr diagnostic software (LiDat) or a compatible scan tool, then operate the machine through a complete warm-up cycle to verify the repair and ensure no code recurrence.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Liebherr service manual for your specific model and consider engaging a certified Liebherr technician for complex electrical diagnostics or if you're uncomfortable performing these procedures.