What is XCMG XE Series (6D125-6D140-6D170-CM850-CM2850) Fault Code 261?

Fault Code 261 indicates an Injector Cylinder #6 - Mechanical System Not Responding Properly or Out of Adjustment. This code is triggered when the Engine Control Module (ECM) detects that the fuel injector for cylinder #6 is not operating within the expected mechanical parameters, either due to incorrect calibration, mechanical failure, or communication issues between the ECM and the injector solenoid.

This fault is critical for XCMG excavators equipped with Cummins CM850 or CM2850 engines (commonly paired with Komatsu 6D series engines in these models) because proper injector response directly affects fuel delivery, combustion efficiency, and overall engine performance. When cylinder #6 fails to respond correctly, it can lead to power loss, excessive smoke, and potential damage to the exhaust aftertreatment system.

Common Symptoms

• Check Engine Light illuminated on the dashboard with stored fault code 261
• Rough idling or engine misfiring, particularly noticeable under load or during hydraulic operations
• Black or white smoke from the exhaust, indicating incomplete combustion in cylinder #6
• Power derate mode activated, limiting engine RPM and reducing excavator productivity
• Increased fuel consumption due to inefficient combustion in the affected cylinder

Potential Causes

• Faulty injector solenoid on cylinder #6 due to internal coil failure or mechanical sticking
• Worn or damaged injector wiring harness, especially at rub points near the valve cover or along the engine block—common in used machines with 5,000+ hours
• Corroded or loose electrical connectors at the injector or ECM, particularly in machines exposed to moisture or extreme environments
• Low fuel pressure caused by a failing fuel pump or clogged fuel filters, affecting injector response
• ECM calibration drift or software issues requiring reprogramming
• Mechanical injector wear, including stuck plungers or damaged nozzles in high-hour excavators

How to Troubleshoot and Fix Code 261

Step 1: Visual Inspection
Inspect the wiring harness for cylinder #6 injector, checking for abrasion, cuts, or corrosion at connection points. On used excavators, pay special attention to areas where harnesses contact engine components or the frame. Check the injector connector for moisture, corrosion, or bent pins.

Step 2: Electrical Testing
Using a digital multimeter, measure the resistance of the cylinder #6 injector solenoid (typically 0.3-0.9 ohms for Cummins CM850/CM2850 engines). Compare readings with other cylinders. Test for voltage supply at the injector connector with the ignition on (should read battery voltage). Check for short circuits to ground.

Step 3: Injector Swap Test
Swap the cylinder #6 injector with another cylinder (e.g., #5). Clear codes and run the engine. If the fault follows the injector, replacement is necessary. If the code remains on cylinder #6, investigate ECM issues or harness problems specific to that circuit.

Step 4: Fuel System Check
Verify fuel pressure meets specifications (typically 35-50 PSI at idle for these engines). Replace fuel filters and check for air in the fuel system, which can cause erratic injector operation.

Step 5: ECM Diagnostics
Use Cummins INSITE or compatible diagnostic software to perform injector cutout tests and verify ECM calibration. Update ECM software if outdated versions are detected.

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Disclaimer: This guide provides general troubleshooting steps. Always consult the manufacturer's service manual and consider professional diagnostic services for complex ECM or fuel system issues, especially on used equipment with unknown service history.