What is Sany Excavator Fault Code H055?

Fault Code H055 indicates a malfunction in the hydraulic pump solenoid circuit, specifically detecting an abnormal electrical signal or open circuit in the pump control system. This code is triggered when the Electronic Control Module (ECM) detects voltage irregularities, current flow issues, or complete signal loss from the hydraulic pump's proportional solenoid valve.

For Sany excavators, this is a critical fault because the hydraulic pump solenoid directly controls main pump displacement and system pressure. When H055 activates, the machine may enter a protective derate mode to prevent hydraulic system damage, significantly impacting productivity and operational efficiency.

Common Symptoms

When fault code H055 is active, operators typically experience:

• Illuminated warning light on the instrument cluster, often accompanied by an audible alarm
• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Erratic or sluggish movement of hydraulic cylinders, particularly during combined operations
• Engine RPM fluctuations as the ECM attempts to compensate for pump control issues
• Complete loss of hydraulic function in severe cases where the solenoid circuit is completely open

Potential Causes

The most common technical reasons for H055 appearing on used Sany excavators include:

• Damaged wiring harness near the hydraulic pump mounting area, where vibration and heat cause insulation breakdown
• Corroded or loose connector pins at the solenoid valve plug, especially on machines operating in wet or coastal environments
• Failed proportional solenoid coil within the pump assembly due to age-related deterioration or electrical overload
• ECM internal fault affecting the solenoid driver circuit (less common but possible in higher-hour machines)
• Chafed wires at known rub points between the main frame and rotating platform

How to Troubleshoot and Fix Code H055

Step 1: Visual Inspection Begin by thoroughly inspecting the wiring harness from the ECM to the hydraulic pump solenoid. On used excavators, focus on areas where the harness passes through metal grommets or near moving components. Check for abraded insulation, pinched wires, or oil contamination that can cause short circuits.

Step 2: Connector and Resistance Testing Disconnect the solenoid connector at the pump. Inspect pins for corrosion, bent terminals, or moisture intrusion. Using a digital multimeter, measure solenoid coil resistance (typically 8-15 ohms for Sany systems). Check harness continuity from the connector back to the ECM pins specified in the service manual.

Step 3: Voltage Supply Verification With the ignition on (engine off), measure supply voltage at the solenoid connector using your multimeter. You should see battery voltage (12-14V) on the power supply pin. If voltage is absent, trace the circuit back through any relay modules or fuses in the electrical distribution box.

Step 4: Solenoid Functional Test If resistance and voltage are correct, the solenoid itself may have internal mechanical failure. Replace the proportional solenoid valve and clear codes using Sany diagnostic software or a compatible CAN bus scanner. For used machines, always replace the mating connector if corrosion is present to prevent recurring faults.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual for your specific model and consider professional diagnostic assistance for complex electrical issues.