What is Doosan DX220LC-9C Fault Code E520807-12?

Fault Code E520807-12 on the Doosan DX220LC-9C excavator indicates a "Swing Motor 2 Pressure Sensor Circuit - Voltage Below Normal or Shorted to Low Source." This diagnostic trouble code (DTC) signals that the Electronic Control Unit (ECU) has detected abnormally low voltage or a short circuit to ground in the electrical circuit connected to the second swing motor pressure sensor.

This code specifically monitors the swing system's hydraulic pressure feedback, which is critical for the machine's upper structure rotation control. The DX220LC-9C utilizes dual pressure sensors to precisely regulate swing acceleration, deceleration, and load compensation. When sensor voltage drops below the manufacturer's specified threshold (typically below 0.5V), the ECU logs this fault to prevent erratic swing behavior and potential component damage. For used excavators, this code is particularly important as it directly affects operator safety and productivity during slewing operations.

Common Symptoms

• Swing function operates erratically or exhibits reduced speed and power during rotation
• Dash warning light illuminates (typically a yellow diagnostic indicator or specific swing system alert)
• ECU may activate derate mode, limiting swing motor performance to prevent hydraulic system damage
• Intermittent or complete loss of smooth swing deceleration and cushioning
• Abnormal hydraulic noise from the swing motor assembly during operation

Potential Causes

The most common technical causes for E520807-12 on used DX220LC-9C excavators include:

• Damaged or corroded wiring harness at known rub points near the swing bearing or center joint (especially where the harness passes through the rotating platform)
• Failed swing motor pressure sensor due to internal component degradation or seal failure allowing moisture intrusion
• Shorted sensor connector pins caused by corrosion, bent terminals, or water infiltration in the multi-pin connector
• Broken or frayed wires in the sensor signal circuit between the sensor and main ECU
• ECU internal fault (rare) affecting the sensor voltage supply or signal processing circuit
• Poor ground connection at the swing motor assembly mounting points due to paint buildup or rust

How to Troubleshoot and Fix Code E520807-12

Step 1: Visual Inspection Begin with a thorough physical examination of the swing motor pressure sensor and its wiring harness. On used excavators, focus on areas where the harness routes through the swing bearing center joint—a notorious wear point on the DX220LC-9C. Check for chafed insulation, exposed copper wire, oil contamination, or connector corrosion. Inspect the sensor connector for pushed-out pins, moisture, or physical damage.

Step 2: Electrical Testing Disconnect the pressure sensor connector and use a digital multimeter to check sensor resistance. The Swing Motor 2 pressure sensor should typically read between 200-500 ohms (consult your service manual for exact specifications). Next, measure voltage supply at the harness connector with ignition on—you should see approximately 5V reference voltage from the ECU. Check for continuity between sensor ground and chassis ground (should be less than 1 ohm).

Step 3: Circuit Diagnosis With the sensor disconnected, measure voltage on the signal wire at the ECU connector. If voltage remains below 0.5V with the sensor disconnected, you have a short to ground in the wiring harness. Carefully trace the wire path, especially through flex points and the center joint, using a test light or continuity tester to locate the short.

Step 4: Component Replacement If wiring tests normal but the sensor resistance is out of specification, replace the swing motor pressure sensor. For used machines, always apply dielectric grease to connector pins during reassembly to prevent future corrosion. If the harness shows wear, replace the affected section or install protective loom covering at friction points.

Step 5: System Verification Clear the fault code using Doosan G-SCAN diagnostic software or an equivalent CAT/Doosan-compatible scan tool. Operate the swing function through full rotation cycles and monitor live sensor data to confirm proper voltage range (typically 0.5V-4.5V under varying pressure conditions).

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Disclaimer: This guide provides general troubleshooting information for experienced diesel mechanics. Always consult the official Doosan service manual for your specific serial number and software version. If you're unfamiliar with electrical diagnostics or hydraulic systems, contact a certified Doosan technician to prevent injury or further equipment damage.