What is XCMG XE490D (CM2150C-CM2150D) Fault Code 155?

Fault Code 155 indicates a Coolant Temperature Sensor Circuit malfunction in the Cummins CM2150 ECM (Engine Control Module). This code specifically triggers when the ECM detects an abnormal voltage signal from the engine coolant temperature (ECT) sensor circuit, typically reading values outside the expected 0.5-4.5 volt range.

The CM2150C and CM2150D engines used in XCMG excavators rely heavily on accurate coolant temperature data for fuel injection timing, fan control, and engine protection strategies. When this sensor circuit fails, the ECM cannot properly regulate engine temperature, potentially leading to overheating, performance derate, or cold-start issues. For used excavators, this code often appears due to sensor degradation, corroded connectors, or damaged wiring harnesses—common issues in machines with 3,000+ operating hours.

Common Symptoms

• Check Engine Light (CEL) illuminated on the instrument panel with reduced engine power
• Engine fan running continuously at high speed, even when coolant temperature is normal
• Hard starting or rough idle when engine is cold, as ECM defaults to substitute temperature values
• Engine derate mode activated, limiting machine to 50-70% power output to prevent thermal damage
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions

Potential Causes

The most common technical causes for Code 155 on used XCMG excavators include:

• Failed coolant temperature sensor due to internal resistance drift or element corrosion (common after 5+ years)
• Damaged wiring harness at known rub points near the engine block mounting brackets or valve cover
• Corroded or loose connector pins at the ECT sensor connection (moisture intrusion is frequent in excavators)
• ECM internal circuit failure affecting the 5-volt reference supply to the sensor
• Poor ground connection at the engine block ground strap, causing voltage signal interference
• Coolant contamination causing sensor element fouling or electrical short circuits

How to Troubleshoot and Fix Code 155

Step 1: Visual Inspection Begin by inspecting the ECT sensor (typically located near the thermostat housing on the CM2150). Check for coolant leaks, corrosion on the sensor body, and damaged wiring. On used excavators, examine the wire harness for abrasion points where it contacts the engine block or frame—this is a common failure point.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance. A functional ECT sensor should read approximately 2,000-3,000 ohms at 70°F (21°C). Next, check the ECM supply voltage at the harness connector—you should see 4.8-5.2 volts on the signal wire with key on, engine off. If voltage is absent or incorrect, suspect ECM or harness issues.

Step 3: Connector and Harness Verification Inspect the connector pins for corrosion, bent terminals, or moisture. Clean with electrical contact cleaner and apply dielectric grease. Check harness continuity from sensor to ECM using a multimeter—resistance should be less than 5 ohms. Look for intermittent shorts by wiggling the harness while monitoring resistance.

Step 4: Component Replacement If the sensor tests faulty, replace with an OEM Cummins ECT sensor (part number 4921744 or equivalent). For used machines, always replace the connector pigtail simultaneously to prevent future corrosion issues. After installation, clear codes using Cummins INSITE diagnostic software and perform a test cycle.

Step 5: Final Verification Run the engine through a full heat cycle while monitoring live data with diagnostic software. Verify the ECM receives smooth temperature readings from 60°F to 200°F without dropouts or spikes.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official XCMG and Cummins service manuals for your specific machine serial number. If unfamiliar with electrical diagnostics or working with diesel engine management systems, seek assistance from a certified Cummins technician to avoid damage to sensitive ECM components.