What is Sany Excavator Fault Code P955?

Fault Code P955 indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal temperature reading in the hydraulic system. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects a signal from the hydraulic oil temperature sensor that falls outside the manufacturer's specified range, or when the circuit shows an open, short, or intermittent connection.

The hydraulic oil temperature sensor monitors the operating temperature of the hydraulic fluid, which is critical for maintaining optimal viscosity and system efficiency. When hydraulic oil temperature exceeds safe operating limits or the sensor fails to report accurate data, the ECM may initiate protective measures including performance deration or system shutdown to prevent catastrophic damage to pumps, motors, and seals. For Sany excavators, especially used machines with higher operating hours, this code requires immediate attention as prolonged operation with compromised hydraulic temperature monitoring can lead to accelerated component wear and costly repairs.

Common Symptoms

• Warning light illuminated on the instrument cluster, often accompanied by a hydraulic temperature icon
• Reduced hydraulic performance or derated engine power to protect the system from overheating
• Intermittent loss of hydraulic function, particularly during high-demand operations like digging or lifting
• Abnormal hydraulic oil temperature readings on the display (either extremely high or low values that don't match actual conditions)
• ECM logging the fault code even when hydraulic oil feels normal to touch during manual inspection

Potential Causes

• Hydraulic oil temperature sensor failure due to internal element degradation or contamination exposure
• Damaged or corroded wiring harness between the sensor and ECM, common in used excavators with harness routing near hot engine components
• Poor electrical connections at the sensor connector, often caused by moisture intrusion, corrosion, or loose terminals
• ECM software glitch or calibration issue requiring parameter reset or firmware update
• Actual hydraulic system overheating due to restricted oil cooler, low oil level, or failing cooling fan (triggering legitimate high-temperature warnings)
• Chafed wires at known rub points near the hydraulic tank or along the boom structure

How to Troubleshoot and Fix Code P955

Step 1: Visual Inspection Begin with a thorough visual examination of the hydraulic oil temperature sensor located on the hydraulic tank. Check the sensor connector for corrosion, bent pins, moisture, or loose connections. Inspect the wiring harness from the sensor to the ECM for signs of abrasion, especially where it passes near moving components or hot surfaces—a common issue in used excavators.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures. Compare readings against Sany specifications (typically 2,000-3,000 ohms at room temperature). Check for voltage supply at the connector (usually 5V reference voltage from the ECM). Test the circuit for continuity and shorts to ground along the entire harness length.

Step 3: Component Replacement and Verification If the sensor tests faulty, replace it with a genuine or OEM-equivalent hydraulic oil temperature sensor. For used excavators, always apply dielectric grease to connector terminals before reassembly to prevent future corrosion. Clear the fault code using diagnostic software compatible with Sany systems, then monitor during operation to confirm the repair. If the code returns, investigate ECM functionality or potential software issues.

Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper tools and training.