What is Sany Excavator Fault Code P873?

Fault Code P873 indicates a malfunction in the Auxiliary Hydraulic Pressure Sensor Circuit, specifically detecting an abnormal voltage signal or sensor performance issue. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) receives voltage readings outside the expected range from the auxiliary hydraulic pressure sensor, typically below 0.5V or above 4.5V on a standard 5V reference circuit.

In Sany excavators, the auxiliary hydraulic pressure sensor monitors the pressure in optional hydraulic circuits used for attachments like breakers, grapples, or augers. This sensor provides critical feedback to the ECM to optimize hydraulic flow, prevent system overload, and protect the hydraulic pump from damage. When P873 activates, the machine may enter a protective derate mode to prevent catastrophic hydraulic system failure, significantly impacting productivity on job sites.

Common Symptoms

When fault code P873 is active, operators typically experience:

• Auxiliary hydraulic function warning light illuminated on the instrument cluster or monitor display
• Reduced or erratic auxiliary hydraulic flow to attachments, causing inconsistent performance
• Complete loss of auxiliary hydraulic functions while main boom and bucket operations remain normal
• Intermittent fault code that appears and disappears, especially during temperature changes or machine vibration
• ECM derate mode limiting engine RPM or hydraulic pump output in severe cases

Potential Causes

The most common technical reasons for P873 in used Sany excavators include:

• Damaged or corroded sensor connector at the auxiliary hydraulic manifold, especially on machines with high operating hours in wet or corrosive environments
• Failed auxiliary hydraulic pressure sensor due to internal diaphragm rupture or electronic component degradation
• Wiring harness damage along known rub points near the auxiliary hydraulic valve bank or along the boom structure
• ECM supply voltage issues affecting the 5V reference circuit to multiple sensors
• Contaminated hydraulic oil causing sensor membrane fouling or pressure spike damage
• Loose or corroded ground connections in the sensor circuit creating intermittent voltage fluctuations

How to Troubleshoot and Fix Code P873

Step 1: Visual Inspection and Connector Check Begin by locating the auxiliary hydraulic pressure sensor on the hydraulic manifold block. Disconnect the sensor connector and thoroughly inspect for corrosion, bent pins, moisture intrusion, or oil contamination. On used excavators, this connector is particularly vulnerable to environmental damage. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnecting.

Step 2: Sensor Voltage and Resistance Testing Using a digital multimeter, check the 5V reference voltage at the sensor connector with the key on and engine off. You should measure approximately 4.8-5.2V on the reference wire. Next, measure sensor ground continuity (should be less than 1 ohm resistance to battery negative). With the sensor connected, backprobe the signal wire and observe voltage while starting the engine—it should range between 0.5V (low pressure) and 4.5V (high pressure) during normal operation.

Step 3: Harness Inspection for Used Equipment Wear Trace the sensor wiring harness from the sensor back to the main chassis harness, paying special attention to areas where the harness contacts metal edges, clamps, or moves with hydraulic lines. On used Sany excavators, common failure points include the harness routing near the auxiliary valve solenoids and the transition point where cab harnesses enter the main frame. Look for chafed insulation, exposed copper, or previous repair attempts with electrical tape.

Step 4: Sensor Replacement and System Verification If voltage tests indicate sensor failure, replace the auxiliary hydraulic pressure sensor with a genuine Sany or OEM-equivalent part (verify part number compatibility for your specific model year). After installation with a new O-ring seal, clear fault codes using Sany PC diagnostic software or a compatible scan tool. Cycle the auxiliary hydraulics through full pressure range and monitor live data to confirm the sensor reports smooth voltage transitions between 0.5-4.5V.

Step 5: ECM and Advanced Diagnostics If the fault persists after sensor and harness repair, suspect ECM internal issues with the 5V supply circuit or signal processing. This requires factory-level diagnostics with Sany proprietary software to test ECM pin voltage outputs and perform actuator tests. In rare cases on high-hour used machines, hydraulic pressure spikes from worn pumps or contaminated oil can damage sensor circuits—consider hydraulic system pressure testing and oil analysis.

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Disclaimer: This guide provides general diagnostic information for Sany excavator fault code P873. Hydraulic and electrical system repairs should be performed by qualified diesel mechanics or authorized Sany service technicians. Always consult the official service manual for your specific machine model and serial number. Improper repairs may result in equipment damage, warranty issues, or safety hazards.