XCMG XE215C Fault Code 755: Meaning, Symptoms & Fix Guide

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What is XCMG QSX15 Fault Code 755?

XCMG QSX15 Fault Code 755 indicates a fault in the Engine Coolant Temperature (ECT) Sensor Circuit — specifically an out-of-range high voltage signal detected by the Engine Control Module (ECM).

This code is triggered when the ECM receives a voltage signal from the coolant temperature sensor that exceeds the acceptable threshold, typically above 4.75V DC, suggesting an open circuit, failed sensor, or wiring fault rather than an actual overheating condition.

On the Cummins QSX15 engine — which powers many XCMG heavy excavators — coolant temperature data is critical for fuel injection timing, cooling fan control, and engine protection derating. An inaccurate signal can cause the ECM to make incorrect fueling and thermal management decisions, directly impacting machine reliability and longevity.

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Common Symptoms

When Fault Code 755 is active on your XCMG QSX15, operators typically experience the following:

• Warning light illumination on the instrument cluster, often accompanied by an engine protection alert
• Engine derating — reduced power output as the ECM defaults to a protective operating mode
• Inaccurate coolant temperature gauge readings, often pegged at maximum or reading cold regardless of actual engine temperature
• Cooling fan running at full speed continuously due to the ECM defaulting to worst-case thermal assumptions
• Difficulty achieving full hydraulic performance, as power is restricted under the engine protection strategy

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Potential Causes

The following are the most likely technical causes for this fault, particularly on used or high-hour XCMG excavators:

• Failed ECT Sensor — internal open circuit causing signal voltage to spike above range
• Damaged or corroded sensor connector — moisture ingress is common on machines operating in muddy or wet environments
• Chafed or broken wiring harness — harness routing near the engine block or exhaust manifold on QSX15 machines is a known wear point
• Open circuit in the sensor signal wire between the sensor and the ECM connector pin
• ECM pin corrosion or damage — less common but possible on older machines with maintenance history gaps

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How to Troubleshoot and Fix Code 755

Follow this systematic diagnostic procedure before replacing any components.

Step 1 — Inspect the Sensor and Connector Locate the ECT Sensor on the QSX15 engine block (typically near the thermostat housing). Visually inspect the connector for corrosion, bent pins, or moisture. On used excavators, connector degradation is the most overlooked cause — clean terminals with electrical contact cleaner before proceeding.

Step 2 — Check Sensor Resistance Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At ambient temperature (~25°C), a healthy QSX15 ECT sensor should read approximately 2,000–3,000 ohms. An open reading (OL/infinite) confirms a failed sensor.

Step 3 — Perform a Circuit Continuity Check With the sensor disconnected, use your multimeter to test continuity between the sensor harness connector and the corresponding ECM connector pin. Reference the XCMG/Cummins QSX15 wiring diagram for correct pin identification. Any break in continuity confirms a harness fault requiring repair or replacement.

Step 4 — Use Diagnostic Software Connect Cummins INSITE or the XCMG-specific diagnostic tool to monitor live ECT sensor voltage data. A reading consistently above 4.75V with the sensor connected confirms an open circuit in the signal path.

Step 5 — Replace and Verify Replace the faulty component — sensor or harness segment — and clear the fault code. Run the engine to operating temperature and confirm the code does not return and coolant temperature reads correctly.

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⚠️ Disclaimer: This guide is intended for informational and diagnostic reference purposes only. Always consult a certified heavy equipment mechanic or authorized XCMG/Cummins service technician before performing repairs on live machinery. Incorrect diagnosis or repair can result in engine damage, safety hazards, or voided warranties.