Sumitomo SH220LC-5 Fault Code 1625: Complete Diagnostic Guide

What is Sumitomo SH220LC-5 Fault Code 1625?

Fault Code 1625 on the Sumitomo SH220LC-5 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal temperature reading detected by the Engine Control Module (ECM). This code typically appears when the ECM receives voltage signals outside the expected range from the coolant temperature sensor, suggesting either sensor failure, wiring issues, or actual overheating conditions.

The coolant temperature sensor is critical for the SH220LC-5's diesel engine management system. It provides real-time data to the ECM, which adjusts fuel injection timing, idle speed, and activates cooling fan operation. When this sensor circuit fails, the engine cannot properly regulate its operating temperature, potentially leading to reduced performance, increased fuel consumption, or catastrophic engine damage if actual overheating goes undetected.

Common Symptoms

When fault code 1625 is active on your SH220LC-5, operators typically experience:

• Engine warning light illuminated on the instrument cluster with possible temperature gauge reading abnormally high or low
• Cooling fan running continuously at maximum speed, even during cold starts
• Reduced engine power or derate mode activation as the ECM enters failsafe operation
• Difficulty starting the engine, especially in cold weather conditions
• Rough idle or irregular engine RPM as the ECM uses default temperature values

Potential Causes

The most common technical causes for code 1625 on used SH220LC-5 excavators include:

• Faulty coolant temperature sensor with internal resistance degradation (common after 5,000+ operating hours)
• Damaged wiring harness between the sensor and ECM, particularly where the harness routes near the engine block and experiences heat cycling
• Corroded or loose electrical connectors at the sensor or ECM—a frequent issue in machines operating in wet or corrosive environments
• Coolant contamination affecting sensor accuracy or actual engine overheating triggering legitimate warnings
• ECM software glitches or internal ECM failure (less common but possible in high-hour machines)
• Poor ground connection at the sensor mounting point due to rust or debris buildup

How to Troubleshoot and Fix Code 1625

Step 1: Visual Inspection and Initial Checks Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, moisture, or damaged pins. On used excavators, check the wiring harness along its entire route for chafing, particularly where it contacts hot engine surfaces or metal brackets. Clean all connectors with electrical contact cleaner.

Step 2: Sensor Resistance Testing Disconnect the coolant temperature sensor and measure its resistance using a digital multimeter. At room temperature (68°F/20°C), the sensor should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Compare readings at different temperatures—resistance should decrease smoothly as temperature increases. Erratic or out-of-range readings confirm sensor failure.

Step 3: Circuit Voltage and Wiring Tests With the sensor disconnected and ignition on, measure reference voltage at the harness connector. You should see approximately 5 volts from the ECM. Check for continuity between the sensor connector and ECM pins, and verify the ground circuit has less than 1 ohm resistance. For used machines, this is critical—corroded grounds are a primary failure point.

Step 4: Replacement and Verification If testing confirms sensor or wiring failure, replace the defective component using OEM or quality aftermarket parts. After installation, clear the fault code using diagnostic software (Sumitomo-compatible scan tool) and monitor coolant temperature readings during a full warm-up cycle. Verify the cooling fan cycles properly and the code doesn't return.

Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Sumitomo service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics on used heavy equipment, contact a certified Sumitomo technician to prevent further damage or safety hazards.