What is XCMG XE750D Fault Code E264(3) SPN970 FMI31?

XCMG XE750D Fault Code E264(3) SPN970 FMI31 indicates a critical issue with the Engine Coolant Temperature (ECT) sensor circuit, specifically reporting "Voltage Above Normal or Shorted to High Source" (FMI 31). This diagnostic trouble code (DTC) means the Engine Control Module (ECM) is detecting an abnormally high voltage signal from the coolant temperature sensor circuit, typically above 4.5-5.0 volts when normal operating range should be 0.5-4.5 volts.

SPN 970 specifically references the engine coolant temperature sensor system, which is critical for proper fuel injection timing, engine protection protocols, and hydraulic oil temperature management on the XE750D. When this sensor circuit fails, the ECM cannot accurately monitor engine thermal conditions, potentially leading to overheating damage or unnecessary engine derating that reduces machine productivity on job sites.

Common Symptoms

• Check Engine Light or Engine Warning Lamp illuminated on the instrument cluster with visible fault code display
• Engine derate mode activated, limiting maximum RPM to approximately 1500-1800 RPM to protect the engine
• Cooling fan running continuously at high speed, even when engine is cold or at normal operating temperature
• Difficulty starting in cold weather conditions due to ECM defaulting to a fixed temperature value (typically 176°F/80°C)
• Erratic temperature gauge readings or gauge stuck at maximum reading despite actual engine temperature

Potential Causes

Damaged or corroded wiring harness is the most common issue in used XE750D excavators, particularly where the sensor harness routes near the exhaust manifold or rubs against the engine block during normal vibration.

Failed Engine Coolant Temperature (ECT) sensor with internal short circuit, especially in machines with 5,000+ operating hours where sensor elements degrade from thermal cycling.

Shorted sensor connector pins due to moisture intrusion, coolant leaks contaminating the electrical connection, or physical damage from improper maintenance procedures.

ECM internal circuit failure (rare but possible in high-hour machines) where the 5-volt reference circuit develops internal shorts.

Aftermarket or incorrect replacement sensors installed during previous repairs that don't meet XCMG OEM specifications for resistance values.

How to Troubleshoot and Fix Code E264(3) SPN970 FMI31

Step 1: Visual Inspection and Connector Check Locate the ECT sensor on the engine block (typically near the thermostat housing on XE750D models). Disconnect the sensor connector and thoroughly inspect for corrosion, bent pins, coolant contamination, or moisture. On used excavators, check the entire harness routing for wear points, abrasion damage, or evidence of previous repairs with electrical tape. Clean connectors with electrical contact cleaner and dielectric grease.

Step 2: Sensor Resistance Testing Using a digital multimeter (DMM), measure the resistance across the ECT sensor terminals with the sensor removed from the engine. At 68°F (20°C), resistance should read approximately 2,400-2,700 ohms; at 176°F (80°C), approximately 270-300 ohms. Compare readings to XCMG specifications. If readings are infinite (open circuit) or near zero ohms, replace the sensor with genuine XCMG parts (part number specific to XE750D).

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition ON (engine OFF), measure voltage at the harness connector (engine side). The ECM should supply approximately 5.0 volts on the signal wire. If voltage reads above 5.2 volts or fluctuates erratically, suspect wiring short to battery voltage or ECM fault. Check harness continuity to ECM pins using wiring diagrams and repair any shorts. For used machines, pay special attention to harness sections that may have been pinched during previous engine work.

Step 4: Advanced Diagnostics Connect XCMG diagnostic software (XCMG Excavator Diagnosis System) via the machine's diagnostic port to monitor live ECT sensor data and verify the ECM is processing signals correctly. Clear codes after repairs and perform a loaded engine test to confirm proper temperature readings under operating conditions.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official XCMG XE750D service manual and follow proper safety procedures. If you're uncomfortable performing electrical diagnostics on used heavy equipment, consult a certified XCMG dealer or qualified diesel technician to prevent further damage or safety hazards.