What is Sany SY365H Fault Code H105?

Fault Code H105 on the Sany SY365H excavator indicates a hydraulic pump control solenoid valve malfunction or abnormal signal in the main hydraulic system. This code is triggered when the Electronic Control Unit (ECU) detects an electrical circuit fault, voltage irregularity, or communication error with the hydraulic pump flow control solenoid.

The SY365H relies on precise electronic control of its variable displacement hydraulic pump to match engine power with hydraulic demand. When H105 appears, the machine's load-sensing system cannot properly modulate pump output, directly impacting boom speed, swing torque, and overall cycle times. For used excavators, this code frequently points to degraded wiring harnesses or contaminated hydraulic pilot circuits rather than catastrophic pump failure.

Common Symptoms

• Reduced hydraulic power across all functions, particularly noticeable during combined operations (e.g., boom lift while swinging)
• Intermittent or permanent derate mode where engine RPM is limited to protect the drivetrain
• Hydraulic system warning light illuminated on the dash panel, often accompanied by audible alarms
• Erratic pump response with delayed or "hunting" behavior when controlling attachments
• Increased fuel consumption due to the ECU defaulting to high-pressure standby mode as a failsafe

Potential Causes

The H105 code on used SY365H machines typically stems from these technical failures:

• Solenoid valve coil resistance out of specification (normal range: 18-22 ohms) due to heat cycling and age
• Corroded or oil-contaminated connectors at the pump-mounted solenoid harness (common at the 4-pin Deutsch connector)
• Chafed wiring along the right-side engine bay where harnesses contact the fuel cooler bracket—a known wear point on 2015-2018 models
• Failed ECU voltage supply to the solenoid circuit (requires stable 12V supply; check for voltage drops under load)
• Contaminated hydraulic pilot oil causing mechanical sticking of the spool valve inside the solenoid assembly

How to Troubleshoot and Fix Code H105

Step 1: Perform Visual and Electrical Inspection
Disconnect the battery and locate the hydraulic pump solenoid on the main pump's regulator body (driver's side of engine). Inspect the 4-pin connector for oil intrusion, bent pins, or green corrosion. Use a digital multimeter to check coil resistance—readings outside 18-22 ohms indicate solenoid replacement is needed.

Step 2: Test Circuit Voltage and Grounds
Reconnect the battery and back-probe the solenoid connector with the ignition on (engine off). Verify 12V supply voltage on the power pin and confirm solid ground continuity (less than 0.5 ohms resistance to chassis). For used excavators, trace the harness along the engine block to find common rub points where insulation may be worn through.

Step 3: Monitor Live Data and Perform Function Tests
Using Sany diagnostic software (SY-LINK) or compatible scan tool, monitor solenoid PWM duty cycle while operating hydraulics. Normal operation shows 20-80% modulation. If readings are erratic or stuck at 0%, check the ECU output driver and inspect for water damage inside the main controller box (located under the operator seat).

Step 4: Hydraulic System Checks
If electrical tests pass, drain a sample of pilot hydraulic oil from the pump regulator. Metal particles or dark, oxidized oil indicate internal valve contamination. Replace the pilot filter and flush the circuit before reinstalling or replacing the solenoid valve assembly.

---

Disclaimer: This guide provides general troubleshooting information for the Sany SY365H fault code H105. Hydraulic and electrical system diagnostics should be performed by qualified heavy equipment technicians. Always consult the manufacturer's service manual and follow proper lockout/tagout procedures before servicing.