Sany SY365-8 Fault Code 37: Complete Diagnostic Guide

What is Sany SY365-8 Fault Code 37?

Fault Code 37 on the Sany SY365-8 excavator indicates a Main Pump Solenoid Valve Circuit Malfunction, specifically affecting the hydraulic system's electronic proportional control valve. This diagnostic trouble code (DTC) signals that the Electronic Control Module (ECM) has detected an abnormal voltage or current reading in the main hydraulic pump's solenoid circuit, which directly controls pump displacement and system pressure.

This code is critical because the main pump solenoid valve regulates hydraulic flow based on operator input and load demand. When this circuit malfunctions, the SY365-8 cannot properly modulate hydraulic power, leading to reduced machine performance and potential protection mode activation. The Sany controller continuously monitors this circuit for open circuits, short circuits, or resistance values outside the 8-25 ohm specification range.

Common Symptoms

When Code 37 is active on your SY365-8, operators typically experience:

• Hydraulic system operating in reduced power mode with noticeably slower cycle times across all functions
• Intermittent or complete loss of hydraulic responsiveness, particularly during combined multi-function operations
• Engine RPM fluctuations when attempting heavy lifting or digging operations
• Warning light illumination on the instrument cluster, often accompanied by audible alarm
• Erratic boom, arm, or bucket movements that don't correspond smoothly to joystick inputs

Potential Causes

The most common technical causes for Code 37 on used SY365-8 excavators include:

• Damaged wiring harness near the main pump mounting area where vibration and hydraulic oil contamination cause insulation breakdown
• Corroded connector pins at the solenoid valve plug, especially on machines operating in wet or coastal environments
• Failed proportional solenoid coil within the main pump assembly (resistance outside 8-25 ohm specification)
• ECM internal driver circuit failure, particularly on high-hour machines (6,000+ hours)
• Chafed wires at known rub points where the harness passes through the swing bearing area
• Contaminated hydraulic oil causing solenoid valve spool sticking and abnormal current draw

How to Troubleshoot and Fix Code 37

Step 1: Initial Visual Inspection Begin by inspecting the main pump solenoid connector located on the pump body. Disconnect the connector and examine pins for corrosion, bent terminals, or oil contamination. On used excavators, this connector frequently suffers from hydraulic fluid intrusion. Clean with electrical contact cleaner and verify pin tension.

Step 2: Electrical Testing Using a digital multimeter (DMM), measure solenoid coil resistance directly at the valve. With the connector disconnected and ignition off, check resistance between the two solenoid terminals—specification is 8-25 ohms. Values below 5 ohms indicate a short circuit; infinite resistance confirms an open circuit requiring solenoid replacement.

Step 3: Harness Continuity Check Test the wiring harness from the ECM connector (typically located in the cab) to the pump solenoid. Check for continuity on both wires and verify no short-to-ground conditions. Pay special attention to harness routing near the swing motor and through frame pass-throughs where abrasion commonly occurs on used machines.

Step 4: Voltage Supply Verification With ignition on and engine running, backprobe the solenoid connector to verify the ECM is supplying proper voltage (typically 12V PWM signal). If voltage is present but the solenoid tests good, suspect ECM driver circuit failure.

Step 5: Clear Code and Monitor After repairs, clear the fault code using Sany diagnostic software or by disconnecting the battery for 30 seconds. Operate the machine through full hydraulic functions and monitor for code recurrence.

---

Disclaimer: This guide provides general diagnostic procedures for Sany SY365-8 excavators. Hydraulic system repairs involve high-pressure components and electrical systems. Always consult the official Sany service manual and consider professional technician assistance for complex repairs, especially on used equipment where multiple wear-related issues may coexist.