Sumitomo SH290-5 Fault Code 1625: Technical Guide

What is Sumitomo SH290-5 Fault Code 1625?

Fault Code 1625 on the Sumitomo SH290-5 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting an abnormal voltage signal or open circuit condition in the sensor wiring harness.

This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) receives voltage readings outside the normal operating range (typically 0.5-4.5V) from the coolant temperature sensor. The ECT sensor is critical for the SH290-5's Isuzu engine management system, as it directly influences fuel injection timing, idle speed control, and engine protection protocols. When this code activates, the ECM enters a default mode using pre-programmed temperature values, which can significantly impact engine performance and fuel efficiency.

Common Symptoms

Operators experiencing Code 1625 typically report:

• Engine warning light illuminated on the instrument cluster with potential hard fault alarm
• Difficult cold starting or extended cranking periods, especially in cooler weather
• Poor fuel economy and black smoke from exhaust due to improper fuel mixture compensation
• Engine running rough at idle or failing to reach normal operating temperature
• Cooling fan running continuously at maximum speed regardless of actual engine temperature

Potential Causes

The most common technical failures triggering Code 1625 on used SH290-5 excavators include:

• Damaged or corroded ECT sensor connector – particularly common where the harness passes near the turbocharger heat shield
• Failed coolant temperature sensor – internal thermistor degradation after 5,000+ operating hours
• Broken or shorted wiring in the sensor harness, especially at known rub points near the engine mount brackets
• Corroded ECM pins at connector C-123 (engine harness connection point)
• Low coolant level exposing the sensor tip, creating false readings
• Contaminated coolant causing sensor element fouling or electrical resistance changes

How to Troubleshoot and Fix Code 1625

Step 1: Visual Inspection Begin by inspecting the ECT sensor location on the engine block (typically near the thermostat housing on Isuzu engines). Check for coolant leaks, corrosion on the two-pin connector, and ensure the wiring harness isn't damaged from rubbing against engine components – a common issue on used machines with deteriorated harness clips.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the ECT sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Compare readings against the temperature-resistance chart in the Sumitomo service manual. Next, check for continuity in the harness wiring from sensor to ECM connector C-123 (pins typically 2-17 and 2-32).

Step 3: Voltage Signal Verification With the ignition ON (engine off), backprobe the ECT sensor connector and measure the reference voltage from the ECM – it should read approximately 5 volts. If voltage is absent, trace the harness for breaks or check ECM power supply circuits. For used excavators, pay special attention to connector corrosion and harness chafing at the valve cover routing point.

Step 4: Component Replacement If sensor resistance is out of specification or the harness shows damage, replace the faulty component using genuine Sumitomo/Isuzu parts (part number typically 8-97318-685-0 for ECT sensor). After replacement, clear codes using diagnostic software and verify proper operation through a complete heat cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo SH290-5 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause engine damage or void warranties on refurbished components.