What is Sany Excavator Fault Code P104?

Fault Code P104 on Sany excavators indicates a hydraulic pump solenoid valve circuit malfunction, specifically detecting an abnormal voltage or current signal in the main pump control system. This code is generated when the Electronic Control Module (ECM) identifies that the electrical circuit controlling the hydraulic pump's variable displacement solenoid is operating outside manufacturer-specified parameters, typically between 0.5-4.5 volts.

This fault is critical because the hydraulic pump solenoid directly regulates pump flow and pressure, which controls all excavator functions including boom, arm, bucket, and swing operations. When P104 triggers, the ECM may force the machine into a protective derate mode to prevent catastrophic hydraulic system damage. For used Sany excavators, this code frequently appears due to age-related electrical degradation in the pump control harness or solenoid coil deterioration from heat cycles and contamination exposure.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably slower cycle times on boom and arm movements
• Intermittent loss of hydraulic response, where controls become unresponsive for 2-5 seconds before resuming
• Amber or red warning light illuminated on the instrument cluster, often accompanied by audible alarm
• Engine RPM fluctuation when attempting heavy lifting operations as the ECM tries to compensate for pump control loss
• Complete hydraulic system shutdown in severe cases, with only engine operation remaining functional

Potential Causes

The most common technical causes for P104 in used Sany excavators include:

• Solenoid valve coil failure due to internal short circuits or open windings (resistance should measure 8-15 ohms)
• Damaged wiring harness near the main pump mounting area where vibration causes wire chafing against metal brackets
• Corroded or loose connector pins at the pump solenoid plug, especially on machines operated in wet or coastal environments
• ECM internal driver circuit failure affecting the solenoid output channel
• Contaminated hydraulic oil causing solenoid spool sticking, which increases electrical current draw beyond specifications
• Voltage supply issues from the machine's main power distribution, particularly worn battery cables or alternator problems

How to Troubleshoot and Fix Code P104

Step 1: Initial Electrical Verification Connect a multimeter to the solenoid connector (engine off). Measure coil resistance between the two solenoid terminals—readings should be 8-15 ohms. If open circuit (infinite resistance) or short circuit (under 5 ohms), replace the pump solenoid valve. Check supply voltage with ignition on: should read 12-14V DC.

Step 2: Harness and Connector Inspection Physically trace the wiring harness from the ECM to the pump solenoid, focusing on areas where the harness contacts frame rails or hydraulic lines. On used excavators, inspect for wire insulation wear, oil contamination on connectors, and verdigris corrosion on pins. Clean connectors with electrical contact cleaner and apply dielectric grease.

Step 3: Dynamic Circuit Testing Using Sany diagnostic software (PC Suite or equivalent), monitor live solenoid command values while operating controls. Compare commanded current (typically 300-800 mA) against actual current. A variance greater than 15% indicates solenoid mechanical binding or ECM driver issues. Perform a solenoid actuation test through the software to verify response.

Step 4: Hydraulic System Verification Check hydraulic oil condition and pump case drain flow. Contaminated oil can cause solenoid internal sticking. Verify pump case drain flow doesn't exceed 1.5 LPM at operating temperature, which would indicate internal pump wear affecting solenoid operation.

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Disclaimer: This guide provides general troubleshooting information. Always consult Sany service manuals and qualified hydraulic technicians for complex repairs. Improper diagnosis can lead to expensive component damage.