What is Sany Excavator Fault Code E104?

Fault Code E104 on Sany excavators indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal hydraulic oil temperature reading. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects either an open circuit, short circuit, or implausible signal from the hydraulic oil temperature sensor.

The hydraulic system is the lifeblood of any excavator, and maintaining optimal oil temperature (typically 50-80°C or 122-176°F) is critical for component longevity and performance. When the ECM cannot accurately monitor hydraulic oil temperature, it compromises the machine's ability to protect itself from overheating damage, reduced hydraulic efficiency, and accelerated seal degradation. For Sany excavators—especially used units operating in demanding conditions—this code requires immediate attention to prevent catastrophic hydraulic system failure.

Common Symptoms

When Code E104 is active, operators typically experience:

• Warning light or error message displaying E104 on the instrument cluster or monitor panel
• Reduced hydraulic performance, including slower cycle times and decreased lifting capacity
• Intermittent or complete loss of hydraulic functions during operation
• Engine derate mode activation, limiting RPM to protect the hydraulic system
• Abnormal hydraulic pump noise or cavitation sounds due to temperature-related viscosity changes

Potential Causes

The most common technical causes for E104 in used Sany excavators include:

• Faulty hydraulic oil temperature sensor due to internal element failure or contamination exposure
• Damaged wiring harness at known rub points near the hydraulic tank or pump mounting area
• Corroded or loose connector pins at the sensor or ECM interface (common in machines with 3,000+ hours)
• Short circuit to ground caused by harness chafing against frame components
• ECM internal fault or corrupted calibration data (rare, but possible in older units)
• Actual hydraulic oil overheating due to clogged coolers, low oil level, or excessive ambient temperatures

How to Troubleshoot and Fix Code E104

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank or return line). Inspect the wiring harness for visible damage, abrasion, or contact with moving parts. Check the connector for corrosion, bent pins, or oil contamination—extremely common in used excavators operating in wet or dusty environments.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (should typically read 2,000-3,000 ohms at 20°C; consult Sany specifications). Test the harness continuity from sensor connector to ECM. Check for short circuits to ground by measuring resistance between each wire and chassis ground (should read infinite resistance/open circuit).

Step 3: Live Data Analysis Connect Sany diagnostic software or a compatible scan tool to monitor live hydraulic oil temperature readings. Compare the displayed value against an infrared thermometer reading of the actual hydraulic tank. A variance greater than 10°C indicates sensor drift or failure.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Sany temperature sensor or OEM-equivalent part. For used machines, always apply dielectric grease to connector pins during reassembly to prevent future corrosion. Clear the fault code and perform a function test under load to verify repair.

Critical for Used Equipment: Before replacing expensive components, thoroughly inspect harness routing for modifications from previous repairs. Check for aftermarket attachments or poorly secured hydraulic lines that may have altered original wire paths, creating new rub points.

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Disclaimer: This guide provides general troubleshooting information. Hydraulic and electrical system diagnosis requires proper training and tools. Always consult the official Sany service manual and consider professional technician assistance for complex repairs, especially on high-hour used equipment.