What is Sany Excavator Fault Code P079?

Fault Code P079 on Sany excavators indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting an abnormal voltage signal or open/short circuit condition. This code is generated when the Engine Control Module (ECM) receives sensor readings outside the normal operating range (typically 0.5-4.5 volts), preventing accurate monitoring of engine temperature.

The ECT sensor plays a critical role in Sany's electronic control system by providing real-time coolant temperature data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection protocols. When P079 triggers, the ECM enters a default mode using predetermined temperature values, which can compromise engine efficiency and longevity, particularly in used machines where cooling system integrity may already be compromised.

Common Symptoms

• Check Engine Light or Engine Warning Lamp illuminated on the instrument cluster
• Engine running rich or lean due to incorrect fuel mixture calculations based on faulty temperature data
• Difficulty starting when the engine is cold, or prolonged cranking times
• Engine fan running continuously at high speed regardless of actual coolant temperature
• Reduced engine power or derate mode activation to prevent potential overheating damage

Potential Causes

The most frequent causes of P079 in used Sany excavators include:

• ECT sensor failure due to internal element degradation or contamination from old coolant
• Damaged or corroded wiring harness connections at the sensor plug, especially near engine vibration points
• Chafed or pinched sensor wires rubbing against engine components or frame edges (common wear point behind the thermostat housing)
• Corroded or loose ground connections affecting circuit continuity
• ECM internal fault (rare, but possible in high-hour machines)
• Coolant contamination causing sensor element coating and inaccurate readings

How to Troubleshoot and Fix Code P079

Step 1: Visual Inspection Begin by inspecting the ECT sensor connector located near the thermostat housing. Check for corrosion, moisture intrusion, bent pins, or physical damage. In used excavators, this connection often shows green corrosion due to coolant leaks—clean with electrical contact cleaner and dielectric grease.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should read approximately 2,000-3,000 ohms (consult Sany service manual for exact specifications). Check wiring harness continuity from sensor connector to ECM—should show less than 5 ohms resistance. Test for short to ground on both signal and reference wires.

Step 3: Voltage Signal Check With the ignition on and sensor connected, backprobe the signal wire. You should see approximately 5V reference voltage. If voltage is absent, trace harness routing for damage, particularly where cables pass through bulkheads or near moving components.

Step 4: Component Replacement If sensor resistance is out of specification or harness shows damage, replace the faulty component. For used machines, always replace the sensor connector pigtail simultaneously, as brittle insulation is common. Clear codes using Sany diagnostic software or compatible scan tool and verify repair with a test cycle.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Sany service manual for your specific model. If unfamiliar with electrical diagnostics, seek assistance from a qualified heavy equipment technician to avoid ECM damage or misdiagnosis.