What is XCMG XE490D CM2150 Fault Code 1679?

Fault Code 1679 indicates a Low Voltage Detected on the Engine Speed/Position Sensor Circuit (Crankshaft Position Sensor). This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects voltage levels below the manufacturer's specified threshold on the crankshaft position sensor signal wire.

The CM2150 series ECM relies on the crankshaft position sensor to determine engine speed, crankshaft angle, and cylinder position for precise fuel injection timing and engine synchronization. On used XCMG excavators, this fault compromises engine performance, potentially causing starting difficulties, rough running, or complete shutdown. The CM2150's advanced monitoring system flags this code when sensor voltage drops below approximately 0.2-0.3 volts during cranking or operation.

Common Symptoms

• Hard starting or no-start condition, especially after the machine has been sitting or in cold weather
• Engine Check Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Rough idle, misfiring, or inconsistent engine RPM during operation
• Sudden engine stalling or unexpected shutdowns, particularly under load
• Power derate mode activated, limiting hydraulic function and travel speed

Potential Causes

The most common technical causes for Code 1679 on used XCMG excavators include:

• Damaged or corroded crankshaft position sensor connector due to moisture intrusion, especially near the bell housing area where debris accumulation is common
• Worn or frayed sensor wiring harness at known rub points along the engine block or frame rails
• Failed crankshaft position sensor internal coil or magnetic pickup deterioration from heat cycling and age
• Poor ground connection at the ECM or engine block ground strap corrosion
• ECM internal fault (less common) affecting the sensor's 5-volt or 8-volt reference supply circuit
• Excessive air gap between sensor tip and crankshaft reluctor ring caused by sensor mounting looseness or wear

How to Troubleshoot and Fix Code 1679

Step 1: Visual Inspection Begin with a thorough physical inspection of the crankshaft position sensor and wiring harness. Locate the sensor (typically mounted on the engine block near the flywheel housing). Check for oil contamination, physical damage, loose mounting bolts, or connector corrosion. On used excavators, pay special attention to harness chafing points where the wiring runs along frame members or near moving components.

Step 2: Connector and Wiring Testing Disconnect the sensor connector and inspect pins for corrosion, bent terminals, or moisture. Using a digital multimeter (DMM), check for continuity between the sensor connector and the ECM connector (typically 3 wires: signal, 5V/8V reference, and ground). Resistance should be less than 5 ohms. Also verify the sensor's internal resistance (typically 200-1000 ohms between signal and ground terminals, consult service manual for exact specs).

Step 3: Voltage Supply and Sensor Gap Verification With ignition on, measure the reference voltage at the sensor connector (should read 5V or 8V depending on CM2150 configuration). Check the air gap between the sensor tip and reluctor ring teeth using a feeler gauge—specification is typically 0.020-0.050 inches (0.5-1.3mm). If readings are out of specification, replace the sensor and verify proper torque on mounting hardware.

Step 4: Advanced Diagnostics Use Cummins INSITE or compatible diagnostic software to monitor live sensor data during cranking. The signal should show consistent AC voltage pulses (typically 0.5-5V amplitude). Clear codes after repairs and perform a road test under load to confirm the fix.

Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-pressure fuel systems and engine electronics.