What is Sany Excavator Fault Code P371?

Fault Code P371 indicates a malfunction in the hydraulic pump control system, specifically related to abnormal current or voltage signals being sent to the main pump solenoid valve. This code is triggered when the Electronic Control Module (ECM) detects that the electrical current flowing to the pump's proportional control solenoid is outside the manufacturer's specified range, typically between 200-1000mA depending on load demand.

In Sany excavators, the main hydraulic pump is the heart of all machine functions—from boom and arm movements to swing and travel operations. The ECM continuously monitors and adjusts pump displacement through proportional solenoid valves to match operator demand with engine power. When P371 appears, the system cannot properly regulate hydraulic flow, directly impacting machine performance and fuel efficiency. This is particularly critical in used machines where electrical connections and solenoid coils have experienced years of vibration and thermal cycling.

Common Symptoms

• Sluggish hydraulic response across all functions, with noticeably slower cycle times
• Engine RPM fluctuations or unusual hunting at idle when hydraulics are activated
• Automatic power derate mode engaging, limiting engine output to protect the system
• Intermittent loss of hydraulic power, especially when the machine reaches operating temperature
• Warning lamp illumination on the instrument cluster with potential audible alarm

Potential Causes

The most common technical causes for P371 in used Sany excavators include:

• Solenoid coil failure due to internal winding shorts or opens (resistance should measure 3-6 ohms typically)
• Corroded or damaged connectors at the pump solenoid harness—a known wear point where the harness passes near the pump housing
• Chafed wiring along the main harness routing between the ECM and hydraulic pump, particularly where it contacts the frame rail
• ECM driver circuit failure, though less common than field-level issues
• Contaminated hydraulic oil causing solenoid valve sticking, which increases current draw
• Voltage supply issues from corroded ground points or damaged power distribution circuits

How to Troubleshoot and Fix Code P371

Step 1: Visual Inspection and Connector Check Begin by inspecting the pump solenoid connector for corrosion, bent pins, or oil intrusion. Disconnect the harness and examine both male and female terminals. On used excavators, this connector often shows green corrosion due to moisture ingress. Clean with electrical contact cleaner and apply dielectric grease.

Step 2: Solenoid Resistance Testing Using a digital multimeter, measure resistance across the solenoid coil terminals with the connector disconnected. Compare readings to service manual specifications (typically 3-6 ohms). Readings significantly higher indicate coil deterioration; near-zero readings suggest internal shorts.

Step 3: Voltage and Current Testing With the ignition on and engine running, backprobe the solenoid connector using a multimeter to verify supply voltage (should be approximately 12V). Use a clamp ammeter to measure actual current draw during operation—excessive current (above 1200mA) indicates mechanical binding or solenoid failure.

Step 4: Harness Continuity Check Trace the wiring harness from the ECM to the pump, checking for chafe points, especially where it passes through bulkheads or near moving components. Perform continuity tests and check for shorts to ground. In used machines, harness damage accounts for approximately 40% of P371 occurrences.

Step 5: Component Replacement and Verification If testing confirms solenoid failure, replace with genuine Sany parts to ensure proper current characteristics. After replacement, clear codes using diagnostic software and perform a hydraulic function test under load to verify repair.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual for your specific model and serial number. Complex electrical diagnostics should be performed by qualified technicians with appropriate training and tools.