What is Sany Excavator Fault Code P174?

Fault Code P174 indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit - High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor, typically above 4.8 volts, suggesting an open circuit or sensor failure.

The ECT sensor plays a critical role in Sany excavators by monitoring engine coolant temperature and relaying this data to the ECM. This information directly affects fuel injection timing, throttle response, cooling fan operation, and overall engine protection strategies. When P174 activates, the ECM enters a failsafe mode using a default temperature value, which can significantly impact machine performance and fuel efficiency.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the dashboard
• Engine running in cold-start mode continuously, causing rough idling and poor fuel economy
• Cooling fan running constantly at high speed regardless of actual engine temperature
• Reduced engine power or derated performance to prevent potential overheating damage
• Difficulty starting the engine, particularly in cold weather conditions
• Abnormally high or frozen temperature gauge readings on the instrument cluster

Potential Causes

The most common technical causes for Code P174 in used Sany excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire abrasion near engine mounting points or valve covers
• Failed coolant temperature sensor with internal circuit breakage (common after 5,000+ operating hours)
• Corroded or loose electrical connectors at the sensor or ECM terminals due to coolant leaks or moisture intrusion
• Damaged sensor ground wire or poor grounding connection to the engine block
• ECM internal circuit failure (rare, but possible in older machines with electrical system surges)
• Previous repair attempts with incorrect sensor specifications or aftermarket parts incompatible with Sany systems

How to Troubleshoot and Fix Code P174

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block or thermostat housing. Check for coolant leaks, connector corrosion, or physical damage. On used excavators, carefully examine the wiring harness for signs of rubbing against engine components, especially near vibration points.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms. Next, check for continuity between the sensor signal wire and ECM connector. Measure voltage at the disconnected harness connector; you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If resistance readings are out of specification or show infinite resistance (open circuit), replace the ECT sensor with a genuine Sany part. For used machines, always apply dielectric grease to connector terminals before reassembly to prevent future corrosion. Clear the fault code using Sany diagnostic software or a compatible scanner, then monitor the system during a complete heat cycle to confirm proper operation.

Disclaimer: This guide provides general troubleshooting information. For complex electrical diagnostics or if problems persist, consult a certified Sany technician or authorized service center to prevent potential engine damage.