Sany Excavator Fault Code P157: Complete Diagnostic Guide

What is Sany General Fault Code P157?

Fault Code P157 indicates a Hydraulic Pilot Pressure Sensor Circuit Malfunction in Sany excavators. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage signal from the pilot pressure sensor, which monitors the hydraulic pilot control system pressure.

The pilot pressure sensor is critical for Sany excavators because it provides real-time feedback to the ECM about operator input through the joysticks and pedals. When this sensor fails or sends erratic signals, the machine cannot properly interpret control commands, directly impacting operational safety and precision. This is especially problematic in used excavators where sensor degradation and wiring harness wear are common issues.

Common Symptoms

When Code P157 is active, operators typically experience:

• Erratic or unresponsive hydraulic controls – joysticks may not respond proportionally to input
• Intermittent loss of auxiliary hydraulic functions (hammer, grapple, or thumb controls)
• ECM warning light illuminated on the instrument cluster
• Reduced hydraulic response speed or inconsistent boom/bucket movements
• Machine may enter derate mode, limiting engine RPM to protect hydraulic system components

Potential Causes

The most common technical causes for P157 in used Sany excavators include:

• Faulty pilot pressure sensor – internal component failure due to age or contamination
• Damaged wiring harness – particularly at known rub points near the operator cab pivot and along the boom
• Corroded or loose electrical connectors at the sensor or ECM terminals
• Contaminated hydraulic pilot oil causing sensor membrane damage
• ECM software glitches or outdated calibration files
• Voltage supply issues – poor ground connections or damaged power supply wires to the sensor

How to Troubleshoot and Fix Code P157

Step 1: Visual Inspection Begin by inspecting the pilot pressure sensor location (typically mounted on the pilot valve block). Check for physical damage, oil leaks, or loose mounting. On used excavators, carefully examine the wiring harness from the sensor to the ECM, paying special attention to areas where harnesses contact metal surfaces or moving components.

Step 2: Electrical Testing Using a digital multimeter, perform voltage and resistance checks. With ignition on (engine off), measure voltage at the sensor connector – you should see approximately 5 volts supply voltage and ground continuity. Check sensor resistance (typically 200-500 ohms when disconnected). Inspect all connector pins for corrosion, bent terminals, or moisture intrusion common in aging machines.

Step 3: Signal Testing and Component Replacement Connect Sany diagnostic software (PC Suite or compatible scanner) to monitor live sensor data. Observe if the pilot pressure signal fluctuates abnormally or remains static. If electrical tests pass but signal data is erratic, replace the pilot pressure sensor. If wiring issues are found, repair or replace the affected harness section rather than bypassing, as this maintains system integrity.

Step 4: System Verification After repairs, clear the fault code, operate all hydraulic functions through full range, and verify the code does not return. Check hydraulic pilot oil filter condition and consider changing if contaminated, as debris can damage replacement sensors.

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Disclaimer: This guide provides general troubleshooting information. Hydraulic and electrical systems can be dangerous. Always consult your Sany service manual and consider professional diagnostic assistance, especially for complex ECM or hydraulic system issues.