What is Sany Excavator Fault Code P374?

Fault Code P374 indicates an abnormal voltage signal or electrical malfunction in the engine coolant temperature (ECT) sensor circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects a voltage reading outside the expected range—typically either too high (open circuit) or too low (short circuit)—from the coolant temperature sensor.

In Sany excavators, the ECT sensor plays a critical role in engine management. It monitors coolant temperature and sends voltage signals to the ECM, which adjusts fuel injection timing, idle speed, and cooling fan operation accordingly. When P374 activates, the ECM may default to a predetermined "limp mode" temperature value, potentially causing suboptimal engine performance, increased fuel consumption, or overheating risks. For used machines with aging electrical systems, this code often points to deteriorated wiring or corroded connectors rather than sensor failure alone.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument panel
• Engine running at higher-than-normal idle speed due to ECM assuming cold-start conditions
• Cooling fan running continuously or not engaging properly
• Reduced engine power or activation of derate mode to prevent potential overheating
• Difficulty starting in cold weather or prolonged cranking times

Potential Causes

• Faulty ECT sensor due to internal element degradation (common in machines with 5,000+ operating hours)
• Damaged wiring harness from rubbing against engine components or frame—particularly near the thermostat housing
• Corroded or loose electrical connectors at the sensor or ECM (prevalent in excavators exposed to moisture or harsh environments)
• Short circuit to ground caused by worn insulation on sensor wiring
• Open circuit from broken wires inside the harness sheath
• ECM internal fault (rare, but possible in older used excavators with electrical system history)

How to Troubleshoot and Fix Code P374

Step 1: Visual Inspection Begin by inspecting the ECT sensor and its wiring harness near the engine block. Look for obvious damage, frayed wires, oil contamination, or corrosion on connector pins. For used excavators, pay special attention to harness routing where vibration or heat may have caused insulation wear.

Step 2: Test Sensor Resistance Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. Compare readings against Sany specifications (typically 2,000-3,000 ohms at 20°C). If readings are infinite (open) or zero (shorted), replace the sensor.

Step 3: Check Circuit Voltage With the ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts (reference voltage from ECM). No voltage indicates a wiring issue or ECM problem.

Step 4: Inspect Wiring Continuity Test continuity between the sensor connector and ECM pins using wiring diagrams. Check for shorts to ground by measuring resistance between each wire and chassis ground (should be infinite).

Step 5: Clear Code and Monitor After repairs, use Sany diagnostic software or a compatible scanner to clear the fault code. Operate the machine through warm-up cycles and monitor for code recurrence.

Disclaimer: This guide provides general troubleshooting steps. Always consult the official Sany service manual for your specific model and consider professional diagnostic assistance for complex electrical issues or ECM replacement.