Sumitomo SH210LC-5LR Fault Code 1625: Complete Diagnostic Guide

What is Sumitomo SH210LC-5LR Fault Code 1625?

Fault Code 1625 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition in the ECM (Engine Control Module) monitoring system. This code is triggered when the coolant temperature sensor sends readings outside the acceptable voltage range (typically 0.5V to 4.5V), preventing the ECM from accurately monitoring engine thermal conditions.

For the Sumitomo SH210LC-5LR equipped with an Isuzu engine, this code is critical because improper coolant temperature readings can cause incorrect fuel mapping, premature engine wear, and potential overheating damage. The ECM relies on accurate temperature data to adjust fuel injection timing, fan engagement, and engine protection protocols. When this sensor fails on used excavators, the machine may enter a derate mode to prevent catastrophic engine damage.

Common Symptoms

When Code 1625 is active on your SH210LC-5LR, you may experience:

• Temperature gauge reading abnormally high, low, or erratic on the instrument cluster
• Cooling fan running continuously at maximum speed, even during cold starts
• Engine derate or reduced power output as the ECM enters protective mode
• Hard starting conditions, especially in cold weather, due to incorrect fuel enrichment
• Check Engine light or warning indicator illuminated on the display panel

Potential Causes

The most common technical causes for Code 1625 on used Sumitomo excavators include:

• Faulty coolant temperature sensor (CTS) due to internal resistance drift or element failure
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connector pins
• Harness chafing near the engine mounting points or routing areas with vibration exposure
• Corroded or loose electrical connectors at the sensor or ECM terminals (common in machines with 5,000+ hours)
• ECM internal circuit failure (rare, but possible in high-hour used machines)
• Coolant contamination causing sensor element coating and inaccurate readings

How to Troubleshoot and Fix Code 1625

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness from sensor to ECM for visible damage, chafing, or corrosion. On used excavators, pay special attention to harness routing near engine mounts where vibration causes insulation wear.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specs). Check for open circuit (infinite resistance) or short circuit (near-zero resistance). Also measure voltage supply at the harness connector—should read approximately 5 volts with ignition on.

Step 3: Connector and Ground Verification Clean all connector pins with electrical contact cleaner and inspect for bent pins or corrosion (extremely common on machines operating in wet/muddy conditions). Verify ground circuit continuity between the sensor ground wire and chassis ground—should read less than 1 ohm resistance.

Step 4: Component Replacement If sensor testing reveals out-of-spec readings, replace the coolant temperature sensor with OEM or quality aftermarket parts. For used excavators, always replace the connector pigtail if corrosion is present. After replacement, clear codes using diagnostic software and perform a heat cycle test to verify proper operation.

Disclaimer: This guide provides general troubleshooting procedures. Always consult the manufacturer's service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics, consult a certified Sumitomo or Isuzu technician to prevent further damage to your excavator's electrical system.