What is Doosan DX150LC-9C Fault Code E520718-12?

Fault Code E520718-12 indicates a hydraulic pump solenoid valve circuit malfunction with an open circuit or short to ground condition in the main control valve system. This diagnostic trouble code (DTC) is triggered when the Electronic Control Unit (ECU) detects abnormal electrical resistance or voltage in the hydraulic pump's proportional solenoid valve circuit, specifically related to the pump flow control system.

In the Doosan DX150LC-9C excavator, this code directly affects the variable displacement hydraulic pump regulation system. The pump solenoid valve controls hydraulic flow output based on operator demand and engine load. When this circuit fails, the ECM cannot properly modulate pump displacement, leading to compromised hydraulic performance and potential damage to expensive hydraulic components if left unaddressed.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, bucket, swing) with noticeably slower cycle times
• Erratic or unresponsive hydraulic controls, particularly during combined operations or under heavy load
• Warning lamp illumination on the instrument cluster, often accompanied by error message display
• Engine RPM fluctuations or inability to maintain proper engine speed during hydraulic operations
• Hydraulic system overheating due to improper pump regulation and excessive bypass flow

Potential Causes

The E520718-12 code typically results from electrical failures rather than mechanical pump issues. Wiring harness damage is extremely common in used DX150LC-9C excavators, particularly where harnesses route near the hydraulic pump mounting area and experience vibration-induced wear. Connector corrosion at the pump solenoid valve connection point frequently occurs due to hydraulic oil mist and moisture exposure in the engine compartment.

Solenoid valve coil failure within the pump assembly itself ranks as the second most common cause, especially in machines exceeding 5,000 operating hours. ECU internal faults are rare but possible in older units. Failed relay contacts in the main power distribution circuit can also trigger this code.

How to Troubleshoot and Fix Code E520718-12

Step 1: Visual Inspection Begin with a thorough inspection of the wiring harness from the ECU to the hydraulic pump solenoid valve. On used excavators, check for harness abrasion points where cables contact frame members or the pump housing. Inspect the connector at the pump for oil contamination, bent pins, or corrosion. Clean connections with electrical contact cleaner and examine seal integrity.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid valve connector and measure coil resistance. Specifications typically range between 8-15 ohms (consult service manual for exact values). Check for continuity to ground on both solenoid wires with the harness disconnected—any reading indicates a short circuit. Measure supply voltage at the connector with ignition on; you should see battery voltage (approximately 24V on this model).

Step 3: Component Testing If wiring checks pass, test the solenoid valve itself by applying controlled voltage directly to verify operation (you should hear an audible click). For used machines, perform a megohm test on the harness to detect insulation breakdown. Check ECU connector terminals for corrosion or loose pins. Use Doosan diagnostic software (DMS-5) to perform active tests and monitor real-time solenoid valve command signals versus actual response.

Step 4: Repair or Replace Replace damaged harness sections with OEM-grade wiring rated for hydraulic system environments. If the solenoid valve coil has failed, replacement of the entire proportional valve assembly is typically required. Always apply dielectric grease to connectors during reassembly to prevent future corrosion.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Hydraulic and electrical system diagnostics require proper training and safety precautions. Always consult the official Doosan service manual and consider professional assistance for complex repairs, especially on used equipment where multiple underlying issues may exist.