What is Liebherr General Fault Code E520?

Fault Code E520 indicates a malfunction in the engine speed sensor circuit or an implausible engine speed signal detected by the Electronic Control Module (ECM). This code is triggered when the ECM receives inconsistent, erratic, or absent signals from the crankshaft position sensor or engine speed sensor, which are critical for monitoring engine RPM and timing fuel injection events.

In Liebherr excavators, the engine speed sensor provides real-time data that the ECM uses to optimize combustion, control fuel delivery, and manage hydraulic pump output. When E520 activates, the machine's performance is directly compromised because the ECM cannot accurately determine engine position or rotational speed. This fault is particularly critical in used machinery where sensor degradation, wiring wear, and connector corrosion are common failure points that disrupt signal integrity.

Common Symptoms

• Engine fails to start or cranks but won't fire due to loss of position reference
• Intermittent stalling or rough idling, especially during cold starts or under load
• Check engine light or fault warning displayed on the operator panel
• Power derate mode activated, limiting engine RPM and hydraulic performance
• Erratic engine behavior including sudden RPM fluctuations or misfiring

Potential Causes

• Faulty crankshaft position sensor or engine speed sensor due to heat exposure or internal component failure
• Damaged wiring harness or corroded connectors, especially at sensor mounting points prone to vibration and moisture
• Worn sensor mounting bracket causing excessive air gap between sensor and reluctor wheel
• Contaminated reluctor wheel (flywheel teeth) with metal debris, oil buildup, or physical damage
• ECM internal fault or software corruption affecting signal processing (less common)
• Poor electrical grounding at sensor or ECM, causing voltage reference issues

How to Troubleshoot and Fix Code E520

Step 1: Visual Inspection Begin by inspecting the engine speed sensor mounted near the flywheel or crankshaft. Check for physical damage, oil contamination, or excessive air gap (typically 0.5-1.5mm). On used excavators, examine the wiring harness from sensor to ECM for chafing, especially where it passes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, measure sensor resistance (typically 200-1000 ohms depending on sensor type). Check for voltage output while cranking the engine—you should see an AC voltage signal (0.5-5V AC). Inspect connector pins for corrosion, bent terminals, or moisture intrusion, which are prevalent in older machines.

Step 3: Signal and Component Verification Connect Liebherr diagnostic software (LiDat) to monitor live sensor data. Verify the ECM is receiving consistent RPM signals. Clean the reluctor wheel to remove debris and inspect for broken or worn teeth. If sensor tests pass but the code persists, check ECM ground connections and consider ECM reprogramming or replacement.

Step 4: Replacement and Calibration Replace the sensor if readings are out of specification, ensuring proper air gap adjustment. For used excavators, always replace associated O-rings and seals to prevent oil leaks that can damage new sensors.

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Disclaimer: This guide provides general diagnostic information. Always consult Liebherr service manuals and qualified technicians for machine-specific procedures and safety protocols.