Kato HD820-3 Fault Code E35: Complete Diagnostic Guide

What is Kato HD820-3 Fault Code E35?

Fault Code E35 on the Kato HD820-3 excavator indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal hydraulic oil temperature reading. This code is triggered when the Electronic Control Module (ECM) detects either an open circuit, short circuit, or out-of-range temperature signal from the hydraulic oil temperature sensor.

The hydraulic oil temperature monitoring system is critical for the HD820-3's performance because excessive heat degrades hydraulic fluid viscosity, reduces system efficiency, and can cause catastrophic damage to pumps, motors, and seals. The ECM uses this sensor data to protect the machine by limiting performance or shutting down operations when temperatures exceed safe thresholds.

Common Symptoms

When Code E35 is active on your Kato HD820-3, operators typically experience:

• Warning light illumination on the instrument panel, often accompanied by an audible alarm
• Reduced hydraulic performance including slower cycle times and weakened digging force
• Machine derate or automatic shutdown if the ECM cannot verify safe operating temperatures
• Erratic temperature gauge readings that fluctuate abnormally or show implausible values (extremely high or low)
• Intermittent code activation that appears and disappears, especially on older machines with corroded connections

Potential Causes

The most common technical causes for E35 on used HD820-3 excavators include:

• Failed hydraulic oil temperature sensor due to prolonged heat exposure or internal component degradation
• Damaged wiring harness near the hydraulic tank where cables experience vibration and abrasion against metal surfaces
• Corroded or loose electrical connectors at the sensor or ECM, particularly common in machines operating in wet or corrosive environments
• Contaminated sensor tip covered in metallic debris, sludge, or varnish buildup from degraded hydraulic fluid
• ECM internal fault or software calibration issues (rare but possible in high-hour machines)
• Actual hydraulic overheating caused by clogged coolers, failed cooling fans, or restricted oil flow

How to Troubleshoot and Fix Code E35

Step 1: Visual Inspection Begin by inspecting the hydraulic oil temperature sensor located on the hydraulic tank. Check the electrical connector for corrosion, bent pins, or oil contamination. On used excavators, examine the wiring harness routing for wear points where cables contact the frame or hydraulic lines.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C for thermistor-type sensors). Compare readings against Kato specifications. Check for continuity in the wiring from sensor to ECM, and test for short circuits to ground (should show infinite resistance).

Step 3: Sensor and Fluid Verification If electrical tests pass, remove the sensor and inspect the sensing element for physical damage or contamination. Check actual hydraulic oil temperature with an infrared thermometer and verify the oil condition—dark, burnt-smelling fluid indicates overheating problems beyond the sensor. Clean or replace the sensor, ensuring proper thread sealant application.

Step 4: System Reset and Monitoring After repairs, clear the fault code using Kato diagnostic software or by disconnecting the battery for 10 minutes. Monitor the system during operation, particularly watching for code recurrence under load conditions that stress the hydraulic system.

For used excavators, always inspect connector seals and apply dielectric grease to prevent moisture intrusion, a leading cause of recurring sensor codes on older machines.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Kato service manual and consider professional technician assistance for complex repairs or safety-critical systems.