What is Sany Excavator Fault Code P957?

Fault Code P957 indicates a malfunction in the hydraulic pump pressure sensor circuit or an abnormal pressure reading detected by the Engine Control Module (ECM). This code specifically relates to the main hydraulic pump's pressure monitoring system, which is critical for maintaining optimal hydraulic flow and preventing system damage.

In Sany excavators, the hydraulic pump pressure sensor continuously monitors system pressure and sends voltage signals to the ECM. When the ECM detects voltage readings outside the normal operating range (typically 0.5-4.5V), or when actual hydraulic pressure doesn't match expected parameters during operation, it triggers P957. This fault is particularly critical because the hydraulic system powers all excavator functions—boom, arm, bucket, and swing operations. Ignoring this code can lead to reduced machine performance, component damage, or complete hydraulic system failure.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably slower cycle times for boom and arm movements
• Warning light illumination on the instrument cluster, often accompanied by an audible alarm
• Intermittent loss of hydraulic function or erratic operation during demanding tasks
• Engine derate mode activation, limiting RPM to protect the hydraulic system from damage
• Error messages displayed on the digital monitor indicating "Hydraulic System Fault" or "Pressure Sensor Error"

Potential Causes

The most common causes of P957 in used Sany excavators include:

• Faulty hydraulic pump pressure sensor due to internal wear, contamination, or electrical failure
• Damaged wiring harness or corroded connectors between the sensor and ECM, especially at routing points near the hydraulic pump where vibration and heat exposure are highest
• Low hydraulic oil level or contaminated fluid causing actual pressure fluctuations that trigger the sensor
• Worn hydraulic pump creating inconsistent pressure delivery that exceeds sensor tolerance ranges
• ECM software issues or calibration drift in older machines with high operating hours
• Hydraulic filter restriction causing pressure spikes or drops during operation

How to Troubleshoot and Fix Code P957

Step 1: Visual Inspection and Basic Checks Begin by checking hydraulic oil level and condition. Low oil or contaminated fluid (dark, milky, or containing metal particles) must be addressed first. Inspect the wiring harness from the pressure sensor to the ECM, looking specifically for chafing points near the hydraulic pump mounting area, damaged insulation, or corrosion on connector pins.

Step 2: Electrical Testing Using a digital multimeter, disconnect the pressure sensor connector and measure resistance across the sensor terminals (typically 250-350 ohms at room temperature for Sany models). Next, check for supply voltage at the harness connector with the key on—you should see approximately 5V reference voltage from the ECM. Inspect ground continuity by measuring resistance between the sensor ground pin and chassis ground (should be less than 1 ohm).

Step 3: Sensor and System Validation Connect Sany diagnostic software (PC Suite or compatible scan tool) to read live sensor data. Compare actual pressure readings against manufacturer specifications during idle and loaded conditions. For used excavators, pay special attention to connector corrosion—clean terminals with electrical contact cleaner and apply dielectric grease. If sensor readings are erratic or out of range despite good electrical connections, replace the hydraulic pump pressure sensor with OEM or quality aftermarket parts.

Step 4: Hydraulic System Assessment If electrical testing shows normal results, perform a hydraulic pressure test using calibrated gauges to verify actual system pressure matches sensor readings. Check the main relief valve setting and inspect the hydraulic pump for wear, especially in machines exceeding 8,000 operating hours.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual for your specific model and consider engaging a certified technician for complex diagnostics and repairs.