What is Liebherr General Fault Code E42?

Fault Code E42 on Liebherr excavators indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal temperature reading that exceeds safe operating parameters. This code specifically relates to the hydraulic system's thermal management, where the Electronic Control Module (ECM) detects either a sensor circuit failure (open/short circuit) or an actual over-temperature condition in the hydraulic oil reservoir.

This fault is critical for Liebherr machines because hydraulic oil temperature directly affects viscosity, component lubrication, and seal integrity. When E42 triggers, the system may limit machine performance to prevent catastrophic hydraulic pump or motor damage. In used excavators, this code often points to degraded sensors or contaminated oil rather than actual overheating, making accurate diagnosis essential before costly repairs.

Common Symptoms

• Hydraulic system derate or reduced performance, with slower cycle times and diminished boom/arm speed
• Warning light illumination on the operator display panel, often accompanied by an audible alarm
• Intermittent loss of hydraulic power, especially during high-demand operations or after extended run times
• Display showing abnormally high or implausible temperature readings (e.g., -40°C or 150°C+)
• Machine may enter limp mode or restrict certain functions to protect hydraulic components

Potential Causes

• Faulty hydraulic oil temperature sensor – common failure point in machines with 5,000+ operating hours
• Damaged or corroded wiring harness at sensor connector, especially where harness routes near hot engine components or experiences frame flex
• Contaminated or degraded hydraulic oil causing actual overheating due to reduced thermal properties
• Blocked hydraulic oil cooler restricting heat dissipation and creating genuine over-temperature conditions
• ECM calibration issues or software glitches in older controller versions
• Poor electrical ground connections at sensor mounting points due to rust or loose hardware

How to Troubleshoot and Fix Code E42

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank or return line). Inspect the sensor connector for corrosion, oil contamination, bent pins, or moisture intrusion. On used excavators, check for harness chafing points where wiring contacts the frame or hydraulic lines during machine articulation.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. Compare readings against Liebherr specifications (typically 2,000-3,000 ohms at 20°C). Test harness continuity from sensor connector to ECM pins and check for shorts to ground. Verify supply voltage (usually 5V reference) at the disconnected harness connector.

Step 3: Sensor and Oil Verification If electrical tests pass, use an infrared thermometer to verify actual hydraulic oil temperature against sensor readings via diagnostic software. Check oil condition for contamination or thermal breakdown. Inspect the hydraulic cooler for blockages and verify fan operation.

Step 4: Component Replacement Replace the temperature sensor if resistance values are out of specification or if physical damage is evident. For used machines, consider replacing connector pigtails even if the sensor tests good, as corrosion often occurs internally. Clear codes using Liebherr diagnostic software and perform a heat cycle test.

Disclaimer: This guide provides general troubleshooting information. Always consult Liebherr service manuals and qualified technicians for your specific machine model and serial number before performing repairs.