What is Sany Excavator Fault Code P357?

Fault Code P357 indicates a malfunction in the hydraulic pump solenoid control circuit, specifically detecting an open circuit or abnormal voltage signal in the pump's electronic proportional control system. This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) detects that the electrical signal to the hydraulic pump's proportional solenoid valve is outside the normal operating parameters (typically 0.5-4.5 volts).

In Sany excavators, the hydraulic pump solenoid regulates flow and pressure by adjusting the pump's swash plate angle based on operator input and load demands. When P357 appears, the ECM cannot properly modulate hydraulic output, which directly impacts machine performance, fuel efficiency, and operational safety. This is particularly critical in used machines where electrical connections and solenoid components experience accelerated wear from environmental exposure and vibration.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably sluggish boom, arm, and bucket movements
• Hydraulic system operating at maximum displacement regardless of joystick input, causing jerky or uncontrollable movements
• Engine RPM fluctuations or unusual surging during hydraulic operations
• Warning light illumination on the instrument cluster, often accompanied by a wrench or diagnostic icon
• Error message displayed on the monitor panel indicating hydraulic system fault

Potential Causes

The most common technical failures triggering P357 in used Sany excavators include:

• Damaged wiring harness between the ECM and hydraulic pump solenoid, particularly at known rub points near the pump mounting bracket and engine firewall
• Failed proportional solenoid valve due to internal coil breakdown or mechanical seizure from contaminated hydraulic fluid
• Corroded or loose electrical connectors at the solenoid connection point, common in machines operating in wet or marine environments
• ECM internal driver circuit failure, though less common than external wiring issues
• Voltage supply problems from the machine's main power distribution, including blown fuses or damaged relay contacts
• Hydraulic fluid contamination causing solenoid valve sticking or intermittent electrical contact

How to Troubleshoot and Fix Code P357

Step 1: Visual Inspection and Connector Check Begin by locating the hydraulic pump solenoid (typically mounted on the main pump assembly). Disconnect the electrical connector and inspect for corrosion, bent pins, moisture intrusion, or oil contamination. On used excavators, pay special attention to connector seal integrity. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnecting.

Step 2: Solenoid Resistance Testing Using a digital multimeter, measure the solenoid coil resistance. Disconnect the harness and test across the solenoid terminals. Typical resistance values range between 8-15 ohms (consult your service manual for exact specifications). Readings showing infinite resistance indicate an open coil, while near-zero readings suggest a short circuit. Replace the solenoid if readings fall outside specifications.

Step 3: Wiring Harness Continuity and Voltage Testing With the ignition on and engine off, backprobe the solenoid connector to check for supply voltage (should read battery voltage, approximately 12-14V). Next, check for ground continuity on the ground circuit. Inspect the entire wiring harness from the ECM to the solenoid, looking for chafing points, particularly where the harness passes through bulkheads or near moving components. In used machines, harness insulation degradation is common.

Step 4: ECM Signal Testing Using Sany diagnostic software or a compatible scan tool, monitor the ECM's command signal to the solenoid while operating hydraulic functions. The signal should vary between 0.5-4.5 volts proportionally with joystick input. If voltage remains constant or shows no signal, the ECM driver circuit may be faulty, requiring ECM replacement or professional repair.

Step 5: Hydraulic Fluid Contamination Check Before replacing components, sample the hydraulic fluid for contamination. Metal particles or water in the fluid can cause solenoid malfunction. Replace filters and fluid if contamination is present.

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Disclaimer: This guide provides general troubleshooting information. Hydraulic and electrical system repairs can be complex and potentially dangerous. Always consult your Sany service manual and consider professional diagnostic assistance, especially for used machines with unknown service history. Improper repairs may cause equipment damage or personal injury.