Sumitomo SH210-6 Fault Code 73: Complete Diagnostic Guide

What is Sumitomo SH210-6 Fault Code 73?

Fault Code 73 on the Sumitomo SH210-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the engine control module (ECM). This code specifically relates to the temperature monitoring system that regulates engine performance, cooling fan operation, and prevents overheating damage.

The coolant temperature sensor sends voltage signals to the ECM, which uses this data to adjust fuel injection timing, idle speed, and activate warning systems. When the sensor circuit experiences an open/short condition or transmits readings outside normal parameters (typically -40°F to 300°F), the ECM triggers Code 73. For the Sumitomo SH210-6's Isuzu diesel engine, accurate coolant temperature monitoring is critical for maintaining optimal combustion efficiency and preventing catastrophic engine damage.

Common Symptoms

When Code 73 is active, operators typically experience:

• Check engine light illuminated on the instrument panel with possible audible warning alarm
• Hard starting or rough idle, especially during cold starts, as the ECM cannot properly adjust fuel delivery
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Reduced engine power or derate mode activation as a protective measure
• Inaccurate temperature gauge readings showing extreme high/low temperatures or erratic fluctuations

Potential Causes

The most common technical reasons for Code 73 on used SH210-6 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged wiring harness near the thermostat housing where vibration causes wire insulation wear and short circuits
• Corroded or loose connector pins at the sensor plug, especially on machines exposed to wet conditions
• Low coolant level causing sensor exposure to air instead of coolant, producing false readings
• Failed ECM (rare) with corrupted temperature input circuitry
• Aftermarket sensor installation with incorrect resistance specifications for the Isuzu engine

How to Troubleshoot and Fix Code 73

Step 1: Visual Inspection Begin by checking coolant level in the radiator and overflow tank—low coolant is the simplest cause. Inspect the coolant temperature sensor (located near the thermostat housing on the engine block) and its wiring harness for physical damage, oil contamination, or connector corrosion. On used excavators, pay special attention to harness routing where it contacts metal surfaces.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Test wiring continuity from the sensor connector to the ECM—resistance should be less than 5 ohms with no shorts to ground.

Step 3: Sensor Replacement and Verification If resistance values are out of specification or wiring shows damage, replace the coolant temperature sensor with an OEM or quality aftermarket part matching Sumitomo specifications. Clear the fault code using diagnostic software (Sumitomo SCS or compatible scan tool) and monitor for code recurrence during a complete heat cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult the Sumitomo SH210-6 service manual and consider professional diagnosis for complex electrical issues or if you're unfamiliar with high-voltage systems.