What is XCMG B3.9-5.9-C8.3 CM2150 Fault Code 1347-4?

Fault Code 1347-4 indicates an "Engine Speed/Position Sensor 1 Circuit - Voltage Below Normal or Shorted to Low Source" condition in the Cummins CM2150 electronic control system. This code triggers when the Engine Control Module (ECM) detects that the voltage signal from the primary crankshaft position sensor has dropped below the acceptable threshold or is experiencing a short to ground.

This sensor is absolutely critical for the CM2150 engine's operation, as it provides real-time data about crankshaft rotational speed and position. The ECM relies on this information to control fuel injection timing, calculate engine RPM, and coordinate overall engine performance. On XCMG excavators equipped with Cummins B3.9, 5.9, or C8.3 engines, this fault can cause immediate performance degradation or complete shutdown, making it a high-priority diagnostic issue.

Common Symptoms

• Engine cranks but fails to start or starts with extreme difficulty and rough idling
• Sudden engine stalling during operation, particularly under load conditions
• Check Engine Light (CEL) illuminated on the instrument cluster with possible amber warning lamp
• Loss of power or engine derate mode limiting machine performance to protect the engine
• Erratic tachometer readings or complete RPM gauge failure on the operator display

Potential Causes

The most common technical causes for Code 1347-4 on used XCMG excavators include:

• Damaged or corroded crankshaft position sensor connector due to exposure to engine heat, oil contamination, or vibration
• Worn or frayed sensor wiring harness, especially at harness routing points near the engine block where abrasion against metal surfaces occurs
• Failed crankshaft position sensor itself, common in machines with over 5,000 operating hours
• Shorted sensor circuit to ground caused by damaged insulation or pinched wiring during previous maintenance
• ECM internal fault (less common) affecting the sensor signal processing circuit
• Corroded or loose ground connections in the engine harness affecting sensor reference voltage

How to Troubleshoot and Fix Code 1347-4

Step 1: Visual Inspection Begin with a thorough physical inspection of the crankshaft position sensor (typically located near the flywheel housing or front timing cover). Check the sensor body for physical damage, oil contamination, or debris buildup. On used excavators, carefully inspect the wiring harness from the sensor to the ECM for signs of abrasion, particularly where the harness contacts engine components or frame members. Look for melted insulation, exposed copper wire, or greenish corrosion on connector pins.

Step 2: Electrical Testing Disconnect the crankshaft position sensor connector and inspect both the sensor and harness sides for corrosion, bent pins, or moisture intrusion. Using a digital multimeter, measure the sensor's resistance, which should typically read between 200-1,000 ohms (consult Cummins CM2150 specifications for exact values). Next, check the supply voltage at the harness connector with the ignition on—you should see approximately 5 volts on the signal wire. Test for continuity to ground on the signal wire; any continuity indicates a short circuit requiring harness repair.

Step 3: Sensor Gap and Mounting Verification If electrical tests pass, verify the air gap between the sensor tip and the reluctor wheel (target wheel on the crankshaft or camshaft). The gap should be 0.020-0.040 inches (0.5-1.0 mm). Excessive gap from worn mounting brackets—common in high-hour used machines—can cause weak signal voltage. Check that the sensor mounting bolt is torqued properly and hasn't backed out from vibration.

Step 4: Advanced Diagnostics Connect Cummins INSITE diagnostic software or compatible diagnostic tool to read live sensor data and monitor voltage patterns during cranking. This will help identify intermittent faults or weak signal strength. For used excavators with multiple fault codes, clear all codes after repairs and perform a road test to confirm the repair eliminated Code 1347-4 specifically.

Critical Note for Used Equipment: Before replacing the crankshaft position sensor, thoroughly clean all electrical connections with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Many 1347-4 codes on older machines resolve with connector maintenance rather than parts replacement.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Cummins CM2150 service manual and qualified diesel technicians for complex diagnostics. Improper repairs may cause engine damage or void warranties on used equipment.