Sany Excavator Fault Code P628: Complete Diagnostic Guide

What is Sany Fault Code P628?

Fault Code P628 indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit - specifically a voltage signal that is too high or intermittent. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage reading from the coolant temperature sensor, typically exceeding 4.8 volts or showing erratic behavior.

The ECT sensor is critical for Sany excavators because it directly influences fuel injection timing, engine warm-up cycles, and hydraulic oil temperature management. When this sensor fails or sends incorrect data, the ECM cannot properly regulate engine performance, potentially causing overheating, poor fuel economy, and reduced hydraulic response in your machine.

Common Symptoms

When Code P628 is active, operators typically experience:

• Check Engine Light or engine warning lamp illuminated on the dashboard
• Hard starting or extended cranking time, especially in cold conditions
• Engine running rich with visible black smoke from the exhaust
• Cooling fans running continuously at maximum speed, even when engine is cold
• Reduced engine power or derate mode activation to prevent potential damage
• Erratic temperature gauge readings fluctuating between cold and hot

Potential Causes

The most common technical causes for P628 in used Sany excavators include:

• Open circuit or damaged wiring in the ECT sensor harness (especially common where wiring passes near hot exhaust components or sharp metal edges)
• Failed ECT sensor with internal resistance breakdown due to heat cycling over time
• Corroded or loose connector pins at the sensor plug (water intrusion is common in excavators)
• Chafed harness at known rub points near the engine block or cooling system routing
• ECM internal fault or poor ground connections affecting sensor signal reference
• Aftermarket sensor compatibility issues if previous repairs used non-OEM parts

How to Troubleshoot and Fix Code P628

Step 1: Visual Inspection Begin with a thorough inspection of the ECT sensor located on the engine coolant outlet housing. Check for physical damage, coolant leaks, or corrosion on the two-pin connector. On used excavators, carefully inspect the entire wiring harness from sensor to ECM for chafing, heat damage, or rodent damage—pay special attention to areas where the harness contacts metal surfaces or passes near the turbocharger.

Step 2: Electrical Testing Using a digital multimeter (DVOM), disconnect the sensor and measure resistance across the sensor terminals. A functional ECT sensor typically reads 2,000-3,000 ohms at room temperature (68°F/20°C). Compare your reading to Sany's specifications. Next, check for voltage supply at the harness connector with the ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Signal Wire and Ground Testing Perform a continuity test from the sensor connector back to the ECM pins (consult wiring diagrams). Check for shorts to battery voltage or ground. Test the ground circuit integrity by measuring voltage drop—it should be less than 0.1 volts. For used machines, remove and clean connector terminals with electrical contact cleaner, as corrosion creates high resistance that mimics sensor failure.

Step 4: Component Replacement and Verification If testing confirms sensor failure, install an OEM-quality ECT sensor with new sealing washer. Torque to specification (typically 15-20 Nm). Clear the fault code using Sany diagnostic software or a compatible scanner. Run the engine through warm-up cycles and monitor live data to verify the sensor reads progressively from cold (around 2.5V) to operating temperature (around 0.5-1.5V).

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Disclaimer: This guide provides general diagnostic information for Sany excavator Code P628. Always consult the specific service manual for your machine model and serial number. If you're uncomfortable performing electrical diagnostics or lack proper tools, consult a certified Sany technician or qualified heavy equipment mechanic to prevent misdiagnosis or further damage.