What is Sany General Fault Code P977?

Fault Code P977 indicates a malfunction in the hydraulic pump solenoid valve circuit, specifically detecting an abnormal voltage or current flow in the proportional control system. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects that the hydraulic pump's proportional solenoid valve is not responding within manufacturer-specified parameters, typically indicating an open circuit, short circuit, or excessive resistance in the control pathway.

This code is critical for Sany excavators because the proportional solenoid valve directly controls hydraulic pump displacement and flow rates. When this system fails, the machine cannot properly regulate hydraulic pressure, leading to compromised performance across all hydraulic functions including boom, arm, bucket, and swing operations. For used excavators, this fault often signals deterioration in electrical components or connections that have experienced years of vibration and environmental exposure.

Common Symptoms

• Reduced hydraulic power across multiple functions, with noticeably slower cycle times for boom and arm movements
• Intermittent loss of hydraulic response, where controls feel sluggish or unresponsive during operation
• Warning light illumination on the instrument cluster, often accompanied by audible alarm
• Engine derating or automatic RPM reduction as the ECM enters protective mode
• Erratic hydraulic performance that worsens with machine temperature changes or after extended operation

Potential Causes

The most common technical causes for P977 in used Sany excavators include:

• Damaged wiring harness near the hydraulic pump mounting area, where constant vibration causes wire insulation breakdown and potential shorts to ground
• Corroded connector pins at the solenoid valve plug, particularly on machines operated in humid or coastal environments
• Failed proportional solenoid valve due to internal coil degradation or contaminated hydraulic fluid causing valve sticking
• ECM internal driver circuit failure, more common in higher-hour machines with electrical system stress
• Voltage supply issues from the main power harness, including poor ground connections at the pump mounting bracket
• Aftermarket hydraulic system modifications that altered electrical load characteristics beyond OEM specifications

How to Troubleshoot and Fix Code P977

Step 1: Visual Inspection and Connector Examination Begin by disconnecting the battery negative terminal for safety. Locate the proportional solenoid valve on the hydraulic pump assembly and carefully inspect the wiring harness for obvious damage, particularly at flex points and routing clamps. On used excavators, check for harness abrasion against metal edges or heat damage from nearby components. Clean all connector pins with electrical contact cleaner and inspect for corrosion or bent terminals.

Step 2: Electrical Testing with Multimeter Using a quality digital multimeter, measure the solenoid coil resistance at the valve connector (disconnected). Typical specifications range from 8-15 ohms depending on valve type; consult your service manual for exact values. Next, check for supply voltage at the harness side connector with ignition on—you should see battery voltage (12-24V depending on system). Test for continuity between solenoid ground and chassis ground, ensuring resistance below 1 ohm.

Step 3: Advanced Diagnostics and Repair Connect Sany diagnostic software (PC Suite or equivalent) to read live data parameters and verify ECM command signals to the solenoid. Monitor PWM (Pulse Width Modulation) signal output while operating hydraulic controls. If electrical tests pass but the code persists, the solenoid valve itself likely requires replacement. For used machines, always replace associated O-rings and seals during solenoid replacement, and flush hydraulic filters to prevent contamination-related failures.

Disclaimer: This guide provides general troubleshooting information. Hydraulic and electrical system repairs should be performed by qualified technicians with appropriate training and tools. Always consult the official Sany service manual for your specific machine model and serial number range before performing repairs.