Sumitomo SH210LC-5LR Fault Code 1173: Complete Diagnostic Guide

What is Sumitomo SH210LC-5LR Fault Code 1173?

Fault Code 1173 on the Sumitomo SH210LC-5LR indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high voltage or open circuit condition. This code is generated when the Electronic Control Module (ECM) receives a voltage signal outside the normal operating range from the coolant temperature sensor (CTS).

The coolant temperature sensor is critical for this excavator's performance because it directly influences fuel injection timing, engine warm-up protocols, and cooling fan activation. When the ECM cannot accurately read coolant temperature, it defaults to conservative fuel maps that can reduce performance and increase fuel consumption. For used SH210LC-5LR excavators, this sensor circuit is particularly vulnerable to age-related degradation.

Common Symptoms

When Code 1173 is active, operators typically experience:

• Warning light illumination on the instrument cluster with possible audible alarm
• Hard starting or extended cranking time, especially in cold weather conditions
• Poor fuel economy and black smoke from the exhaust due to improper fuel mixture
• Engine overheating or cooling fan running continuously, even when engine is cold
• Reduced engine power or activation of derate mode to protect the engine from potential damage

Potential Causes

The most common technical reasons for Code 1173 on used SH210LC-5LR excavators include:

• Faulty coolant temperature sensor with internal open circuit or degraded resistance element
• Damaged wiring harness between the sensor and ECM, particularly at routing points near the engine block where vibration causes wire chafing
• Corroded or loose connector terminals at the sensor plug or ECM connection points
• Open circuit in sensor ground wire or poor chassis ground connection
• ECM internal fault (rare, but possible in high-hour machines with moisture exposure)
• Previous repair attempts using incorrect sensor specifications or aftermarket sensors with incompatible resistance curves

How to Troubleshoot and Fix Code 1173

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for obvious damage, particularly where it routes around sharp edges or contacts hot engine surfaces. Check the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult service manual for exact specifications). If the reading shows infinite resistance (open circuit) or zero ohms (short circuit), replace the sensor.

Step 3: Circuit Verification With the sensor disconnected, check for voltage at the harness connector. You should read approximately 5 volts reference voltage from the ECM. Test continuity between the sensor ground wire and chassis ground—resistance should be less than 1 ohm. For used machines, pay special attention to harness wear points and connector corrosion before replacing components.

Step 4: Final Verification After repairs, clear the fault code using Sumitomo diagnostic software or a compatible scan tool. Run the engine through a complete warm-up cycle and monitor coolant temperature readings in real-time to ensure proper sensor operation.

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