What is XCMG XE6D125-6D140-6D170 CM2350 Fault Code 124?

Fault Code 124 indicates an Engine Position Sensor Circuit - Voltage Above Normal condition in the Cummins CM2350 engine control system. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects abnormally high voltage readings from the crankshaft position sensor or camshaft position sensor circuit, typically exceeding 4.5-5.0 volts when normal operating range should be 0.5-4.5 volts.

This fault is critical for XCMG excavators equipped with the CM2350 engine because the position sensors provide essential timing data for fuel injection events, engine speed calculation, and cylinder identification. When Code 124 activates, the ECM cannot accurately determine crankshaft/camshaft positioning, which directly impacts combustion efficiency, power output, and can trigger protective engine derating to prevent damage.

Common Symptoms

• Check Engine Light illuminated on the instrument cluster with possible derate warning
• Engine cranks but fails to start or experiences extended cranking time before firing
• Rough idle or misfiring during operation, particularly noticeable under load
• Loss of power or engine derating to reduced RPM (typically 1500 RPM or lower)
• Intermittent stalling especially when the machine is cold or during initial startup

Potential Causes

The most common technical causes for Code 124 on used XCMG excavators with CM2350 engines include:

• Damaged sensor wiring harness due to vibration wear, particularly at routing points near the engine block or flywheel housing where cable ties deteriorate over time
• Corroded or moisture-contaminated connectors on the crankshaft/camshaft position sensor circuits—common in machines operating in wet or marine environments
• Failed crankshaft position sensor with internal short circuit causing voltage spike
• Chafed wiring creating short-to-power condition, especially where harnesses contact sharp metal edges or rotating components
• ECM internal fault or poor ECM ground connection causing voltage reference issues (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code 124

Step 1: Visual Inspection Begin with a thorough physical inspection of the crankshaft and camshaft position sensor harnesses. On used excavators, focus on known wear points where the harness passes near the starter motor, alternator bracket, and flywheel housing. Check for frayed insulation, oil contamination, or evidence of rubbing against engine components.

Step 2: Connector and Resistance Testing Disconnect the position sensor connectors and inspect pins for corrosion, bent contacts, or moisture intrusion. Using a digital multimeter, measure sensor resistance—typical values for CM2350 position sensors range from 800-1200 ohms. Check harness continuity from sensor connector to ECM pins, and verify no short-to-power conditions exist (infinite resistance to battery positive).

Step 3: Voltage Testing With ignition on but engine off, backprobe the sensor connector and measure supply voltage from the ECM—should read approximately 5.0 volts. If voltage exceeds 5.2 volts, suspect ECM or wiring fault. Crank the engine while monitoring signal voltage, which should fluctuate between 0.2-4.8 volts as the crankshaft rotates.

Step 4: Component Replacement If sensor resistance is out of specification or voltage testing reveals abnormalities, replace the faulty position sensor with OEM or equivalent quality parts. For used machines with high operating hours (5,000+), consider replacing both crankshaft and camshaft sensors simultaneously, as they typically wear at similar rates. Always apply dielectric grease to connectors during reassembly to prevent future corrosion.

Step 5: Clear Codes and Verify Repair Use Cummins Insite diagnostic software or compatible scan tool to clear fault codes after repairs. Perform a stationary regeneration or run the engine through full operating temperature cycles while monitoring for code recurrence.

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Disclaimer: This guide provides general diagnostic information. Always consult the official XCMG service manual and Cummins troubleshooting procedures for your specific machine serial number. For complex electrical diagnostics or ECM programming, seek assistance from certified Cummins or XCMG technicians.