What is Sany Excavator Fault Code P355?

Fault Code P355 indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting an intermittent or erratic signal from the coolant temperature monitoring system. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) receives voltage readings from the ECT sensor that fall outside the expected range or fluctuate inconsistently during engine operation.

For Sany excavators, this code is critical because the ECM relies on accurate coolant temperature data to manage fuel injection timing, idle speed control, and fan engagement. When P355 is active, the engine management system may default to a fixed temperature value, potentially causing inefficient combustion, increased emissions, and reduced hydraulic system performance due to improper engine warm-up cycles.

Common Symptoms

• Check Engine Light or Engine Warning Indicator illuminated on the dashboard display
• Engine runs excessively rich or lean, resulting in black smoke or rough idling
• Cooling fan runs continuously at high speed, even when engine temperature is normal
• Engine takes longer than usual to reach operating temperature
• Intermittent power loss or hesitation during hydraulic operations, especially under load

Potential Causes

The P355 code in used Sany excavators typically stems from age-related deterioration and environmental exposure. Common causes include:

• Corroded or loose connector pins at the ECT sensor harness connection point
• Damaged wiring harness due to vibration, heat exposure near the engine block, or rubbing against metal components
• Failed ECT sensor with internal resistance drift or intermittent open circuits
• Contaminated coolant causing sensor element fouling or corrosion buildup
• ECM internal fault (rare, but possible in high-hour machines with previous electrical issues)
• Poor ground connection at the sensor or ECM grounding points

How to Troubleshoot and Fix Code P355

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block (typically near the thermostat housing). Check the wiring harness for signs of chafing, heat damage, or oil contamination. Examine the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators exposed to harsh environments.

Step 2: Electrical Testing Using a digital multimeter, disconnect the ECT sensor connector and measure the sensor's resistance at various temperatures. Compare readings against Sany's specifications (typically 2,000-3,000 ohms at 20°C). Check for voltage supply at the harness connector (usually 5V reference voltage from the ECM). Inspect ground continuity between the sensor ground wire and chassis ground—resistance should be below 1 ohm.

Step 3: Signal Monitoring If possible, use Sany diagnostic software or a compatible scan tool to monitor live ECT sensor data while the engine warms up. Look for erratic voltage spikes or dropouts indicating intermittent connections. Wiggle the harness while monitoring to reproduce the fault.

Step 4: Component Replacement Replace the ECT sensor if resistance values are out of specification or if corrosion is evident. For used excavators, also replace the connector pigtail if pins show any wear. After replacement, clear codes and perform a complete warm-up cycle to verify the repair.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator systems.