What is Sany Excavator Fault Code P940?

Fault Code P940 indicates a malfunction in the Hydraulic Pump Flow Control System, specifically related to abnormal current or voltage detected in the pump's proportional solenoid valve circuit. This code is triggered when the Electronic Control Module (ECM) detects that the electrical signal controlling hydraulic pump output falls outside the manufacturer's specified parameters, typically between 0.5-4.5 volts DC.

This fault is critical for Sany excavators because the proportional solenoid valve directly regulates hydraulic flow based on operator input. When this system malfunctions, the machine cannot properly modulate hydraulic power delivery, severely impacting digging force, swing speed, and overall productivity. In used machines, this code often indicates electrical degradation rather than catastrophic mechanical failure.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably slower cycle times and weak digging force
• Erratic or unresponsive controls, where stick, boom, or bucket movements don't match joystick inputs
• Intermittent engine derating or automatic shutdown to protect the hydraulic system
• Dashboard warning light illuminated, often accompanied by audible alarm in the operator cabin
• Inconsistent pump noise, including unusual whining or surging sounds during operation

Potential Causes

The most common causes of P940 in used Sany excavators include:

• Damaged wiring harness near the main pump area, where constant vibration and heat cause insulation breakdown and short circuits
• Failed proportional solenoid valve due to internal coil deterioration or mechanical sticking from contaminated hydraulic fluid
• Corroded electrical connectors at the pump solenoid, especially on machines operated in wet or coastal environments
• ECM voltage supply issues, including failing voltage regulators or poor ground connections
• Hydraulic fluid contamination causing the solenoid valve spool to stick, creating abnormal current draw

How to Troubleshoot and Fix Code P940

Step 1: Visual Inspection Inspect the wiring harness routing from the ECM to the hydraulic pump solenoid valve. Look for abraded insulation, pinched wires, or evidence of rubbing against metal surfaces—common in used excavators with 3,000+ operating hours. Check all electrical connectors for corrosion, moisture intrusion, or bent pins.

Step 2: Electrical Testing Using a digital multimeter, measure resistance across the solenoid valve coil (typically 8-15 ohms for Sany systems). Check supply voltage at the connector with ignition on—should read battery voltage (12-14V). Measure the signal wire voltage during operation using Sany diagnostic software (SY Diagnostics) to verify the ECM is sending proper command signals.

Step 3: Component Testing Disconnect the solenoid and apply direct voltage to verify mechanical operation—you should hear an audible click. Test for internal short circuits by measuring resistance between terminals and ground (should be infinite resistance). On used machines, remove and inspect the valve for varnish buildup or physical damage.

Step 4: Replacement and Verification If testing confirms failure, replace the proportional solenoid valve with OEM or verified aftermarket parts. Clear fault codes and perform a hydraulic system calibration using diagnostic software. Monitor operation for at least one hour under load.

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Disclaimer: This guide provides general troubleshooting information. Always consult Sany service manuals and qualified diesel hydraulic technicians for complex repairs. Improper diagnosis may cause additional system damage.