What is Sany Excavator Fault Code P956?

Fault Code P956 indicates a malfunction in the hydraulic pump solenoid valve circuit, specifically detecting an abnormal current or voltage condition in the proportional control system. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) identifies that the electrical signal to the hydraulic pump's proportional solenoid valve falls outside the manufacturer's specified parameters, typically indicating an open circuit, short circuit, or excessive resistance.

This code is critical for Sany excavators because the proportional solenoid valve directly regulates hydraulic pump output based on operator demand. When this circuit malfunctions, the machine loses precise control over hydraulic flow, severely impacting digging force, swing speed, and overall operational efficiency. In used equipment, this fault often stems from accumulated electrical degradation rather than sudden component failure.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably sluggish boom, arm, and bucket movements
• Erratic or unresponsive controls where hydraulic functions don't match joystick input intensity
• Warning light illumination on the instrument cluster, often accompanied by a diagnostic message on newer display panels
• Engine running normally but hydraulic system performing at significantly reduced capacity
• Intermittent loss of hydraulic function that may temporarily resolve after machine restart

Potential Causes

The most common technical causes for P956 in used Sany excavators include:

• Damaged wiring harness near the hydraulic pump mounting area where cable routing creates friction points against frame components
• Corroded connector pins at the solenoid valve connection, particularly on machines operated in high-moisture or coastal environments
• Failed proportional solenoid valve due to internal coil degradation or contamination from hydraulic fluid ingress
• ECM internal driver circuit failure affecting the solenoid control output channel
• Voltage supply issues from damaged power distribution circuits or poor grounding connections at the pump assembly

How to Troubleshoot and Fix Code P956

Step 1: Visual Inspection Begin by inspecting the wiring harness running from the ECM to the hydraulic pump solenoid valve. On used excavators, check for harness chafing where cables contact the engine block, pump housing, or frame rails. Examine the connector at the solenoid valve for corrosion, bent pins, or moisture intrusion—clean contacts with electrical contact cleaner if contamination is present.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid valve connector and measure resistance across the solenoid coil terminals (typically 8-15 ohms for Sany proportional valves—consult service manual for exact specifications). Check for voltage supply at the harness connector with ignition on (should read battery voltage). Test for short circuits to ground by measuring resistance between each circuit wire and chassis ground (should read infinite resistance).

Step 3: Component and ECM Testing If wiring tests pass, swap the solenoid valve with a known-good unit to isolate component failure. Use Sany diagnostic software (SY Diagnostic Tool) to monitor live solenoid command data versus actual current flow—discrepancies indicate ECM driver circuit issues. For used machines, always inspect the ground connection point at the pump mounting bracket, as corrosion here creates intermittent faults.

Disclaimer: This guide provides general troubleshooting direction for P956 fault codes. Always consult the official Sany service manual for your specific model and serial number. If you lack experience with hydraulic electrical systems, seek assistance from a certified heavy equipment technician to prevent further damage.