What is Sany Excavator Fault Code P804?

Fault Code P804 indicates a malfunction in the hydraulic pump solenoid circuit, specifically a detected electrical short circuit or abnormal voltage condition in the pump control system. This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) detects voltage readings outside the acceptable range for the main hydraulic pump's proportional solenoid valve circuit.

In Sany excavators, the hydraulic pump solenoid regulates flow and pressure based on operator input and load demands. When the ECM identifies irregular electrical signals—typically caused by short circuits, open circuits, or voltage irregularities—it triggers P804 to prevent potential damage to the hydraulic system. This fault directly impacts machine productivity, as the hydraulic system cannot modulate properly, affecting all hydraulic functions from boom operation to swing and travel movements.

Common Symptoms

Operators experiencing Code P804 may notice:

• Reduced hydraulic power across all functions, with sluggish boom, arm, and bucket movements
• Illuminated warning lamp on the dashboard, often accompanied by an audible alarm
• Erratic hydraulic response where functions operate intermittently or unpredictably
• Engine derate mode activation, limiting RPM to protect the system from further damage
• Complete loss of hydraulic function in severe cases where the ECM enters protective shutdown

Potential Causes

The most common technical causes for P804 in used Sany excavators include:

• Damaged solenoid wiring harness due to chafing against frame components or hydraulic lines—a known wear point near the pump housing
• Corroded or loose electrical connectors at the pump solenoid, especially in machines exposed to moisture or stored outdoors
• Failed proportional solenoid valve within the hydraulic pump assembly due to internal coil deterioration
• ECM internal fault or corrupted software requiring reprogramming
• Voltage supply issues from the main power harness or grounding problems at chassis connection points

How to Troubleshoot and Fix Code P804

Step 1: Visual Inspection Begin by thoroughly inspecting the wiring harness running from the ECM to the hydraulic pump solenoid. On used excavators, check for visible abrasion, pinch points, or worn insulation where the harness contacts the frame or hydraulic components. Inspect all connectors for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid connector and measure resistance across the solenoid terminals. Typical specifications range from 8-15 ohms (consult your service manual). Next, check for voltage supply at the connector with the ignition on—should read approximately 12-24V depending on system configuration. Test for proper ground continuity between the solenoid ground wire and chassis ground (should read less than 1 ohm).

Step 3: Component Testing and Software Verification If wiring and voltage checks pass, use Sany diagnostic software to monitor real-time solenoid command signals and actual response. Compare commanded versus actual values to identify ECM communication issues. For used machines, consider that internal solenoid coil degradation is common after 5,000+ operating hours. Replace the solenoid if resistance values are out of specification or if physical damage is evident.

Step 4: Repair and Verification Address identified issues—repair damaged harnesses with proper gauge wire and weatherproof connectors, replace failed solenoids with OEM or quality aftermarket parts, and clean all ground connections. Clear the fault code using diagnostic software and perform a function test under load to verify proper operation.

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Disclaimer: This guide provides general troubleshooting information. Always consult your Sany service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional system damage or safety hazards.