What is Sany General Fault Code P1655?

Fault Code P1655 indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit - High Voltage Condition. This diagnostic trouble code triggers when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor circuit, typically above 4.8-4.9 volts, when normal operating range should be between 0.5-4.5 volts.

This code specifically affects the engine temperature monitoring system, which is critical for proper fuel injection timing, cooling fan activation, and engine protection protocols. On Sany excavators, the ECT sensor directly influences the ECM's ability to manage engine performance and prevent overheating damage. When this circuit fails, the ECM may default to a conservative fuel map, reducing machine productivity and potentially causing unnecessary engine derating.

Common Symptoms

• Engine warning light or check engine light illuminated on the instrument cluster
• Engine operating in reduced power mode (derate) as a protective measure
• Cooling fan running continuously at high speed, even during cold starts
• Difficulty starting the engine, particularly in cold weather conditions
• Rough idle or poor fuel economy due to incorrect fuel-air mixture calculations
• Temperature gauge reading abnormally low or stuck at minimum position

Potential Causes

The most common technical causes for P1655 on used Sany excavators include:

• Open circuit in the sensor wiring harness, often caused by wire breakage near vibration points or cable routing areas
• Corroded or damaged ECT sensor connector, particularly common in machines exposed to harsh environments or water ingress
• Failed coolant temperature sensor with internal short-to-voltage condition
• Chafed wiring rubbing against engine components or frame members—a known issue near the thermostat housing area
• ECM internal fault (less common) causing incorrect voltage reference or signal interpretation
• Poor ground connection at the sensor or ECM, creating voltage reference issues

How to Troubleshoot and Fix Code P1655

Step 1: Visual Inspection Begin by inspecting the ECT sensor connector located near the thermostat housing. Look for corrosion, moisture intrusion, bent pins, or physical damage. On used excavators, carefully examine the wiring harness for signs of rubbing, particularly where it passes near moving engine components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the ECT sensor and measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms. Next, check for voltage at the harness connector with ignition on, engine off—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Circuit Continuity Check Test continuity between the sensor connector and ECM using wiring diagrams specific to your Sany model. Check for short-to-voltage conditions by measuring between the signal wire and battery positive with the sensor disconnected—any voltage reading indicates a wiring fault.

Step 4: Component Replacement If sensor resistance is out of specification or the connector shows significant corrosion, replace the ECT sensor and connector. For used machines, always replace the connector pigtail as preventive maintenance, as corrosion often extends into wire strands. Clear codes using Sany diagnostic software or a compatible scan tool and verify repair.

Disclaimer: This guide provides general troubleshooting information. Always consult factory service manuals and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with high-voltage systems.