Sumitomo SH260LC-6 Fault Code 73: Complete Diagnostic Guide

What is Sumitomo SH260LC-6 Fault Code 73?

Fault Code 73 on the Sumitomo SH260LC-6 excavator indicates a malfunction in the hydraulic oil temperature sensor circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically due to an open circuit, short circuit, or sensor failure.

This code is critical for the SH260LC-6's performance because the hydraulic oil temperature directly affects system efficiency, component longevity, and operational safety. The ECM relies on accurate temperature readings to prevent overheating, adjust hydraulic flow rates, and protect expensive hydraulic components from thermal damage. Ignoring this fault can lead to reduced hydraulic performance, accelerated wear, and potential system failure.

Common Symptoms

When Code 73 is active on your Sumitomo SH260LC-6, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the instrument panel
• Reduced hydraulic response or sluggish operation of boom, arm, and bucket functions
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Intermittent fault code that appears and disappears during operation
• Potential derate mode activation during extended operation, limiting machine performance

Potential Causes

The most common technical reasons for Code 73 appearing on used SH260LC-6 excavators include:

• Failed hydraulic oil temperature sensor due to age, thermal cycling, or internal component degradation
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the hydraulic tank mounting bracket
• Corroded or loose electrical connectors at the sensor or ECM terminals (common in machines with high operating hours)
• Broken or frayed sensor wiring caused by vibration, heat exposure, or improper previous repairs
• ECM internal circuit failure (rare, but possible in older machines with 8,000+ hours)
• Poor ground connection at the sensor mounting point due to rust or paint buildup

How to Troubleshoot and Fix Code 73

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the side or top of the reservoir). Inspect the wiring harness for obvious damage, chafing, or burns. Check the electrical connector for corrosion, bent pins, or oil contamination. On used excavators, pay special attention to harness routing near moving components or hot surfaces.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. The typical resistance range at 68°F (20°C) should be approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Next, check for continuity in the wiring harness from the sensor connector to the ECM. Measure voltage supply at the sensor connector with the ignition on; you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If the sensor resistance is out of specification or the wiring shows opens/shorts, replace the faulty component. When installing a new hydraulic oil temperature sensor, ensure the mounting surface is clean and apply proper thread sealant. For used excavators, replace any corroded connectors and secure the harness away from friction points using proper routing clips. Clear the fault code using Sumitomo diagnostic software or a compatible scan tool, then operate the machine through a full work cycle to verify the repair.

Disclaimer: This guide provides general diagnostic information. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional assistance from a certified technician for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.