What is XCMG B3.9-5.9-C8.3 CM2150 Fault Code 110-31?

Fault Code 110-31 indicates an Engine Coolant Temperature (ECT) Sensor Circuit Voltage Below Normal or Shorted to Ground. This diagnostic trouble code (DTC) means the Engine Control Module (ECM) has detected an abnormally low voltage signal from the coolant temperature sensor circuit, typically below 0.14 volts.

The CM2150 ECM in XCMG excavators equipped with Cummins B3.9, 5.9, or C8.3 engines relies on accurate coolant temperature data to control fuel injection timing, idle speed, and engine protection strategies. When the ECT sensor circuit voltage drops below the calibrated threshold, the ECM cannot accurately monitor engine temperature, potentially leading to improper fuel delivery, failed cold-start enrichment, and inadequate overheat protection. This fault is particularly critical because the ECM may default to a substitute temperature value, affecting engine performance and longevity.

Common Symptoms

• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine runs rough during cold starts or fails to reach optimal operating temperature
• Engine derate mode activated, limiting power output to 75% or lower to protect components
• Excessive black smoke during initial startup due to improper fuel enrichment
• Cooling fan runs continuously at high speed regardless of actual engine temperature

Potential Causes

Shorted or damaged ECT sensor wiring harness is the most common issue in used excavators, especially where harnesses route near sharp edges, hydraulic lines, or the engine block where vibration causes insulation wear.

Failed coolant temperature sensor due to internal short circuit or moisture intrusion into the sensor connector—common in machines with 5,000+ operating hours.

Corroded or loose connector pins at the ECT sensor or ECM connection points, particularly in excavators operated in wet, muddy, or marine environments.

Chafed wiring at known rub points between the engine valley and firewall, or near exhaust manifold mounting brackets where heat cycling degrades insulation.

ECM internal fault (rare) where the sensor supply voltage circuit or ground reference has failed within the control module itself.

How to Troubleshoot and Fix Code 110-31

Step 1: Visual Harness Inspection Begin with a thorough physical inspection of the ECT sensor wiring harness from the sensor (typically located near the thermostat housing) to the ECM connector. On used excavators, check for wire insulation damage, especially where the harness contacts metal brackets, passes through grommets, or routes near moving components. Look for green corrosion, melted insulation, or exposed copper wire.

Step 2: Connector and Sensor Testing Disconnect the ECT sensor connector and inspect both the sensor pins and harness connector for corrosion, bent pins, or moisture. Using a digital multimeter (DMM), measure resistance across the sensor terminals. A functional ECT sensor should read approximately 2,200-2,700 ohms at 68°F (20°C). If resistance is near zero ohms, the sensor is internally shorted and requires replacement.

Step 3: Circuit Voltage and Ground Testing With the ignition ON and sensor disconnected, use your multimeter to check for 5-volt supply voltage on the sensor signal wire at the harness connector (consult wiring diagrams for correct pin identification). Simultaneously, verify the sensor ground circuit has less than 0.1 ohms resistance to battery negative. If supply voltage is absent or ground resistance is high, trace the circuit back to the ECM, checking for damaged wires or poor ECM connector seating.

Step 4: Repair or Replace Components For used excavators, replace any sections of damaged harness using OEM-spec 18-gauge wire with proper heat-shrink connections and protective loom. Apply dielectric grease to connector pins before reassembly to prevent future corrosion. If the sensor tests faulty, install a genuine Cummins ECT sensor (Part# 3969597 or equivalent) with a new O-ring seal and proper torque specification (typically 18-22 lb-ft). Clear codes using Cummins INSITE diagnostic software or a compatible scan tool and verify the fault does not return after a complete heat cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual for your specific machine model and serial number. If you lack proper diagnostic tools or experience with high-voltage electrical systems, seek assistance from a certified Cummins or XCMG technician to avoid equipment damage or personal injury.