What is Doosan DX150LC-9C Fault Code E520706-12?

Fault Code E520706-12 indicates a "Swing Motor Pressure Sensor Circuit - Voltage Below Normal or Shorted to Low Source" condition on the Doosan DX150LC-9C excavator. This code triggers when the Electronic Control Unit (ECU) detects abnormally low voltage from the swing motor pressure sensor circuit, typically below the manufacturer's specified threshold of approximately 0.5 volts.

The swing motor pressure sensor is a critical component in the hydraulic system that monitors pressure levels during swing operations. This sensor provides real-time data to the ECM (Engine Control Module), allowing the machine to optimize hydraulic performance, prevent overload conditions, and protect the swing motor from damage. When this circuit fails, the excavator loses its ability to accurately monitor swing system pressures, potentially leading to reduced efficiency, erratic swing behavior, or protection mode activation.

For the DX150LC-9C model specifically, this fault compromises the machine's ability to perform smooth, controlled swing operations—essential for productive excavation work.

Common Symptoms

• Swing function warning light illuminated on the instrument cluster with possible audible alarm
• Erratic or sluggish swing performance, with inconsistent speed or jerky movements during rotation
• Swing motion may be limited or restricted as the ECU enters a protective derate mode
• Diagnostic trouble code E520706-12 stored in the ECM memory, retrievable via diagnostic software
• Possible hydraulic system overheating during extended swing operations due to improper pressure regulation

Potential Causes

Damaged or corroded wiring harness is the most common issue in used excavators, particularly where the harness routes near the swing motor mounting bracket—a known rub point on DX150LC-9C models. The constant swing motion creates friction that wears through insulation over time.

Faulty swing motor pressure sensor due to internal component failure, contamination from hydraulic fluid leaks, or age-related deterioration of the sensor element.

Poor electrical connections at the sensor connector, often caused by moisture intrusion, corrosion buildup on pins, or loose terminal connections from vibration.

Shorted circuit to ground where damaged wiring contacts the machine frame or hydraulic components, creating a direct path to ground.

ECM internal issues are less common but possible, particularly in high-hour machines where the control module itself may have degraded circuits.

How to Troubleshoot and Fix Code E520706-12

Step 1: Visual Inspection Begin with a thorough inspection of the swing motor pressure sensor and its wiring harness. Access the sensor located on the swing motor assembly. Check for obvious damage, oil contamination, or corroded connectors. On used excavators, pay special attention to the harness routing near pivot points and metal edges where abrasion commonly occurs.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the sensor connector and measure resistance across the sensor terminals. Compare readings against Doosan specifications (typically 250-1000 ohms depending on temperature). Next, check for voltage supply at the harness connector with ignition on—should read approximately 5 volts. Test for continuity to ground; any reading below infinite resistance indicates a short circuit.

Step 3: Circuit Verification Inspect the entire wiring harness from sensor to ECM, checking for pinched wires, damaged insulation, or corroded splice points. Use electrical contact cleaner on all connectors and apply dielectric grease to prevent future corrosion. If wiring shows wear at known rub points, reroute and secure with proper standoffs.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Doosan pressure sensor (Part #400914-00222 or equivalent). Clear fault codes using Doosan DMS diagnostic software or compatible scan tool, then cycle the swing function through full range while monitoring live data.

For used machines, always replace connector pigtails if corrosion is present, as this prevents recurring faults even with new sensors.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Doosan service manual for your specific machine serial number and software version. If unfamiliar with hydraulic systems or electrical diagnostics, seek assistance from a certified Doosan technician to prevent injury or further equipment damage.