What is Sumitomo SH210-5 Fault Code 1173?

Fault Code 1173 on the Sumitomo SH210-5 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) receives a sensor reading outside the expected voltage range, typically above 4.5 volts when normal operating range should be 0.5-4.0 volts.

The coolant temperature sensor plays a critical role in engine management on the SH210-5, directly affecting fuel injection timing, idle speed control, and cooling fan operation. When this sensor circuit fails, the ECM cannot properly regulate engine temperature, potentially leading to overheating, poor fuel economy, and reduced hydraulic system efficiency. For used excavators, this sensor and its wiring harness are particularly vulnerable to heat-related degradation and connector corrosion.

Common Symptoms

• Check engine light or warning lamp illuminated on the instrument cluster
• Engine running rough at cold start or failing to reach proper operating temperature
• Cooling fan running continuously at high speed, even when engine is cold
• Reduced hydraulic performance or sluggish boom/arm response due to ECM entering limp mode
• Difficulty starting in cold weather conditions or excessive white smoke during warm-up

Potential Causes

The most common technical failures causing Code 1173 on used SH210-5 excavators include:

• Open circuit in the coolant temperature sensor wiring harness, often at flex points near the engine block
• Failed coolant temperature sensor (CTS) with internal resistance breakdown
• Corroded or loose electrical connectors at the sensor or ECM terminals
• Damaged sensor wiring from rubbing against engine components or heat shield deterioration
• Short circuit to battery voltage in the sensor signal wire
• ECM internal fault (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code 1173

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the two-pin connector. On used excavators, carefully examine the entire wiring harness from sensor to ECM for chafing, especially where it passes near hot exhaust components or sharp metal edges.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. If reading shows infinite resistance (open circuit) or zero ohms (short circuit), replace the sensor. Check for supply voltage at the harness connector—should read approximately 5 volts with ignition on.

Step 3: Harness Continuity Check With sensor disconnected, test continuity between the sensor connector pins and corresponding ECM terminals using wiring diagrams. Check for shorts to ground or battery voltage. Pay special attention to connector pins for "green corrosion" common in older machines—clean with electrical contact cleaner and apply dielectric grease.

Step 4: Clear Code and Verify After repairs, clear the fault code using Sumitomo diagnostic software or a compatible scan tool. Run the engine through complete warm-up cycle and monitor live sensor data to confirm readings fall within 0.5-4.0 volt range as temperature increases.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual and consider professional diagnostic assistance for complex electrical issues, especially on high-value equipment.