Sumitomo SH350HD-5 Fault Code 1625: Complete Diagnostic Guide

What is Sumitomo SH350HD-5 Fault Code 1625?

Fault Code 1625 on the Sumitomo SH350HD-5 indicates a malfunction in the engine coolant temperature sensor circuit or an out-of-range coolant temperature reading. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects voltage signals from the coolant temperature sensor that fall outside the manufacturer's specified parameters, typically below 0.2V or above 4.8V.

The coolant temperature sensor is critical for the SH350HD-5's engine management system. It directly influences fuel injection timing, throttle response, and cooling fan operation. On used excavators, this code can lead to improper engine warm-up cycles, increased fuel consumption, and potential overheating conditions that may cause catastrophic engine damage if left unaddressed.

Common Symptoms

When Code 1625 is active on your Sumitomo SH350HD-5, operators typically experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by a check engine indicator
• Hard starting conditions, especially during cold weather, due to incorrect fuel mapping
• Cooling fan running continuously at high speed, even when engine temperature is normal
• Poor engine performance including rough idle, hesitation during acceleration, or reduced power output
• Erratic temperature gauge readings on the dashboard, showing unusually high or low readings that don't match actual engine temperature

Potential Causes

The most common technical causes for Code 1625 on used SH350HD-5 excavators include:

• Faulty coolant temperature sensor due to internal resistance drift or element failure (common after 5,000+ operating hours)
• Damaged wiring harness or corroded connectors, particularly at the sensor plug near the thermostat housing where heat and vibration cause deterioration
• Broken or frayed sensor wires at known rub points along the engine block near mounting brackets
• Contaminated coolant causing sensor element coating or corrosion on the sensor threads
• ECM internal fault or poor ground connection at the ECM mounting location
• Open or short circuit in the sensor signal wire between the sensor and ECM connector

How to Troubleshoot and Fix Code 1625

Step 1: Visual Inspection Begin by conducting a thorough visual inspection of the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks around the sensor base, and corrosion on the electrical connector. On used excavators, inspect the wiring harness from the sensor to the ECM for signs of rubbing, heat damage, or rodent damage—common issues in older machines.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 68°F (20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test the sensor circuit voltage at the ECM connector with the sensor disconnected—you should see approximately 5V reference voltage on the signal wire. Check for continuity between the sensor connector and ECM, and verify less than 5 ohms resistance on ground circuits.

Step 3: Component Replacement and Verification If testing reveals sensor failure, replace the coolant temperature sensor using OEM or equivalent quality parts. Before installation on used equipment, clean the sensor mounting threads thoroughly and apply appropriate thread sealant. Inspect the connector terminals for corrosion—replace the connector pigtail if necessary, as corroded pins are common failure points on high-hour machines. After replacement, clear the fault code using diagnostic software (Sumitomo diagnostic tool or compatible heavy equipment scanner) and perform a cold-start test cycle to verify proper operation.

Disclaimer: This guide provides general diagnostic information for Code 1625. Always consult the official Sumitomo service manual for your specific machine serial number and seek assistance from qualified heavy equipment technicians for complex electrical diagnostics or repairs beyond your expertise level.