What is Sany Excavator Fault Code P373?

Fault Code P373 indicates a malfunction in the engine coolant temperature (ECT) sensor circuit, specifically detecting an intermittent or high voltage signal that exceeds normal operating parameters. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) receives voltage readings from the coolant temperature sensor that are inconsistent with expected engine operating conditions, typically above 4.8-4.9 volts.

In Sany excavators, the ECT sensor plays a critical role in engine management by monitoring coolant temperature and providing real-time data to the ECM. This information directly affects fuel injection timing, idle speed control, cooling fan operation, and overall engine performance. When P373 activates, the ECM may default to a predetermined temperature value, potentially causing inefficient combustion and reduced machine productivity.

Common Symptoms

• Check Engine Light or malfunction indicator lamp (MIL) illuminated on the instrument cluster
• Engine running in limp mode or derate condition with reduced power output and limited RPM
• Cooling fan running continuously at high speed, even during cold starts or low-load operations
• Difficulty starting the engine, particularly in cold weather conditions, or extended cranking times
• Erratic temperature gauge readings that fluctuate abnormally or display unrealistic values

Potential Causes

The most common technical causes for P373 in used Sany excavators include:

• Faulty ECT sensor with internal resistance degradation due to age, heat cycling, or contamination exposure
• Damaged wiring harness or connector corrosion at the sensor plug, especially near the engine block where heat and vibration are concentrated
• Intermittent open circuit caused by wiring abrasion at known rub points along the valve cover or near hydraulic lines
• Poor electrical ground connection at the ECM or sensor mounting location
• ECM software issues or internal ECM circuit board failures (less common but possible in high-hour machines)
• Coolant contamination or air pockets affecting sensor accuracy

How to Troubleshoot and Fix Code P373

Step 1: Visual Inspection Begin by conducting a thorough visual examination of the ECT sensor connector and associated wiring harness. Look specifically for corrosion, moisture intrusion, bent pins, or physical damage. On used excavators, check for harness wear at friction points where cables contact the engine block, fuel lines, or mounting brackets.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the ECT sensor connector and measure resistance across the sensor terminals. At room temperature (approximately 68°F/20°C), resistance should typically read between 2,000-3,000 ohms depending on Sany specifications. Check the signal wire voltage with the ignition on, engine off—it should read approximately 5 volts (reference voltage from ECM).

Step 3: Circuit Continuity Check Test continuity between the sensor connector and the ECM pins to identify any open circuits. Inspect ground circuit integrity by measuring resistance between the sensor ground and chassis ground (should be less than 1 ohm). Pay particular attention to connector terminals for corrosion that can create intermittent high-resistance conditions.

Step 4: Component Replacement If sensor resistance is out of specification or the connector shows significant corrosion, replace the ECT sensor with an OEM or quality aftermarket part. When working on used equipment, always replace the connector pigtail simultaneously if any corrosion is present, as this prevents recurring faults.

Step 5: Clear Codes and Verify After repairs, use Sany diagnostic software or a compatible scan tool to clear fault codes and perform a functional test. Monitor live data during warm-up to ensure temperature readings progress smoothly from ambient to operating temperature (typically 180-200°F/82-93°C).

---

Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Sany service manual for your specific model and seek assistance from qualified diesel technicians when working with electronic engine systems. Improper diagnosis can lead to component damage or safety hazards.