What is Sany Excavator Fault Code P390?

Fault Code P390 indicates a malfunction in the hydraulic pump solenoid circuit or proportional control valve system. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects abnormal voltage, current draw, or signal communication from the hydraulic pump control solenoid. In Sany excavators, this solenoid regulates hydraulic flow and pressure to match engine load and operator demand, directly affecting fuel efficiency and hydraulic response.

This code is critical because the proportional control system optimizes pump displacement based on real-time operating conditions. When P390 activates, the excavator may default to a fixed displacement mode or enter derate, significantly reducing productivity and increasing fuel consumption on used machines already experiencing wear.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, swing, and travel speed noticeably slower)
• Warning light illuminated on the instrument panel, often accompanied by audible alarm
• Erratic hydraulic response where attachment movements become jerky or inconsistent
• Increased engine RPM without corresponding hydraulic performance (pump not loading properly)
• Diagnostic display showing P390 or related hydraulic system fault messages

Potential Causes

The most common technical causes for P390 in used Sany excavators include:

• Solenoid coil failure due to heat exposure or internal short/open circuit (resistance typically 8-15 ohms when functional)
• Wiring harness damage at known rub points near the hydraulic pump mounting area or along the main chassis harness
• Corroded or loose connectors at the solenoid or ECM interface, especially on machines operating in wet/corrosive environments
• ECM internal driver circuit failure preventing proper solenoid energization
• Hydraulic contamination causing mechanical binding of the proportional valve spool
• Voltage supply issues from damaged power distribution harness or failing alternator (should read 24V nominal)

How to Troubleshoot and Fix Code P390

Step 1: Visual Inspection Thoroughly inspect the hydraulic pump solenoid connector and wiring harness for physical damage, corrosion, or oil contamination. On used excavators, check for harness wear where cables contact the frame near the pump assembly. Clean connectors with electrical contact cleaner and verify pin integrity.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (should be 8-15 ohms). Check supply voltage at the solenoid connector with ignition on (should read 24V). Perform a voltage drop test on ground circuits—anything above 0.2V indicates poor grounding requiring correction.

Step 3: Advanced Diagnostics Connect Sany-compatible diagnostic software to monitor real-time solenoid command vs. actual current draw. Command the solenoid through active tests while observing amperage (typically 1.5-2.5A). Significant deviation indicates solenoid or ECM driver failure.

Step 4: Component Replacement Replace the proportional solenoid if resistance or current values are out of specification. For used machines, always replace associated O-rings and check hydraulic oil cleanliness (contamination accelerates repeat failures).

Disclaimer: This guide provides general troubleshooting information. Always consult factory service manuals and qualified technicians for your specific machine serial number and configuration. Improper repairs may cause safety hazards or further damage.