Sany Excavator Fault Code H108: Complete Diagnostic Guide

What is Sany Fault Code H108?

Fault Code H108 indicates a hydraulic oil temperature sensor circuit malfunction or abnormal reading in Sany excavators. This diagnostic trouble code (DTC) triggers when the Electronic Control Unit (ECU) detects voltage signals outside the normal operating range from the hydraulic oil temperature sensor, typically between 0.5V and 4.5V.

This code is critical for Sany excavators because the hydraulic system's performance depends heavily on maintaining optimal oil temperature. The ECU uses temperature data to adjust pump displacement, regulate cooling fans, and prevent hydraulic component damage. When H108 appears, the machine may enter a protective derate mode to prevent catastrophic hydraulic system failure.

Common Symptoms

When Code H108 is active, operators typically experience:

• Hydraulic temperature warning light illuminated on the instrument cluster (amber or red)
• Reduced hydraulic power or sluggish boom/arm/bucket movements as the system enters derate mode
• Cooling fan running continuously at high speed, even during light operation or cold starts
• Inaccurate or erratic temperature gauge readings, showing unrealistic values (extremely high or low)
• Machine shutdown in severe cases where the ECU interprets dangerously high temperatures

Potential Causes

The most common technical reasons for H108 on used Sany excavators include:

• Failed hydraulic oil temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor harness connection point near the hydraulic tank
• Damaged wiring harness caused by rubbing against the hydraulic tank mounting bracket or boom pivot area
• Contaminated sensor tip with metal particles, varnish buildup, or hydraulic fluid degradation products
• ECU calibration drift or water intrusion in the main control module (less common but possible in older machines)
• Poor ground connection at the sensor circuit return path

How to Troubleshoot and Fix Code H108

Step 1: Visual Inspection and Connector Check

Begin by locating the hydraulic oil temperature sensor, typically mounted on the side of the hydraulic tank near the return filter. Disconnect the electrical connector and inspect for corrosion, bent pins, or oil contamination. On used excavators, this connector often accumulates moisture due to thermal cycling. Clean with electrical contact cleaner and inspect the wiring harness for chafing or damage along its routing path.

Step 2: Sensor Resistance Testing

Using a digital multimeter (DMM), measure the sensor's resistance between the signal pin and ground. At room temperature (20°C/68°F), most Sany temperature sensors should read approximately 2,000-3,000 ohms. Compare your reading against Sany's specifications for your specific model. If the reading is open circuit (infinite resistance) or shorted (near zero ohms), the sensor has failed internally and requires replacement.

Step 3: Circuit Voltage and Wiring Verification

Reconnect the sensor and back-probe the connector using thin pins. With the ignition on (engine off), measure the supply voltage from the ECU—it should read approximately 5 volts DC. If voltage is absent or significantly low, trace the wiring back to the ECU connector checking for breaks or shorts to ground. For used machines, pay special attention to harness sections near moving components where insulation wear commonly occurs.

Step 4: Sensor Replacement and Calibration

If testing confirms sensor failure, replace with a genuine Sany temperature sensor or verified OEM-equivalent part. Apply thread sealant with Teflon (never pipe dope, which can contaminate hydraulic oil) and torque to specifications (typically 15-20 Nm). After installation, clear the fault code using Sany diagnostic software or a compatible scan tool. Run the machine through a complete warm-up cycle and verify the temperature reading increases gradually and stabilizes at normal operating temperature (typically 50-80°C/122-176°F).

Disclaimer: This guide provides general diagnostic procedures for Sany excavator fault code H108. Always consult your machine's specific service manual and consider professional assistance from certified Sany technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.