What is Sany Excavator Fault Code P857?

Fault Code P857 indicates an abnormal voltage or signal error in the hydraulic pump control system, specifically related to the main pump pressure sensor circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects voltage readings outside the manufacturer's specified range (typically below 0.5V or above 4.5V) from the hydraulic pressure sensor.

In Sany excavators, the main pump pressure sensor continuously monitors system pressure and sends real-time data to the ECM, which adjusts pump displacement and flow to optimize performance and fuel efficiency. When P857 activates, the ECM cannot accurately regulate hydraulic output, potentially causing erratic machine behavior and reduced operational safety. This is particularly critical in used excavators where sensor degradation and wiring harness wear are common.

Common Symptoms

• Hydraulic system derate or noticeable loss of digging/lifting power
• Erratic boom or arm movements with inconsistent speed or jerky operation
• Warning light illumination on the instrument cluster (typically a wrench or engine symbol)
• Intermittent fault activation that clears and returns, especially during temperature changes
• Increased fuel consumption due to the ECM defaulting to safe-mode hydraulic settings

Potential Causes

The most common technical causes for P857 in used Sany excavators include:

• Failed hydraulic pressure sensor due to internal component degradation or contaminated hydraulic fluid exposure
• Damaged wiring harness at known rub points near the pump mounting area or along the main chassis rail
• Corroded or loose connector pins at the sensor plug, especially in machines exposed to moisture or saltwater environments
• Short circuit or open circuit in the sensor signal wire caused by harness chafing against metal edges
• ECM power supply issues affecting the 5V reference voltage to the sensor
• Contaminated hydraulic oil causing sensor membrane failure or pressure port blockage

How to Troubleshoot and Fix Code P857

Step 1: Visual Inspection Begin by inspecting the hydraulic pump pressure sensor and its wiring harness. Check for visible damage, oil contamination on connectors, corrosion on pins, or harness wear at bend points. In used excavators, pay special attention to areas where the harness contacts metal surfaces or moving components.

Step 2: Electrical Testing Using a digital multimeter, check the sensor's supply voltage with the ignition on (engine off). You should read approximately 5V at the sensor connector. Next, measure sensor output voltage while monitoring hydraulic pressure—it should range from 0.5V to 4.5V proportional to system pressure. Check wiring resistance (should be less than 5 ohms) and inspect for short-to-ground conditions.

Step 3: Sensor and Component Replacement If voltage readings are incorrect, disconnect the sensor and test the ECM reference voltage directly. If the 5V supply is present but sensor output is faulty, replace the pressure sensor. Before installation, inspect the sensor mounting port for debris and verify hydraulic oil cleanliness (contamination accelerates sensor failure). Clear the code using Sany diagnostic software and perform a functional test under load.

Step 4: Harness Repair For wiring issues, repair damaged sections with OEM-spec wire and ensure proper routing away from heat sources and sharp edges. Apply dielectric grease to connectors in harsh environments.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual and consider professional diagnostic assistance for complex electrical issues, especially on used equipment with unknown service history.