What is XCMG General Fault Code 91-15?

Fault Code 91-15 on XCMG excavators indicates a CAN Communication Error between the Engine Control Module (ECM) and the Main Controller (display unit). This code specifically signals that the primary control systems are unable to exchange data properly over the Controller Area Network (CAN) bus, which is the digital nervous system of modern excavators.

This fault affects the machine's ability to coordinate engine performance with hydraulic demands, monitor system parameters, and display critical operating information. The CAN bus serves as the communication highway between all major electronic control units, making this code particularly serious for overall machine operation. When communication breaks down, the excavator cannot function as an integrated system, potentially leading to reduced performance, incorrect diagnostic readings, or complete operational shutdown.

Common Symptoms

• Warning lights illuminated on the dashboard, often including the check engine light and communication error indicator
• Display screen shows error messages, goes blank, or displays incorrect/frozen readings for engine RPM, temperature, or fuel level
• Engine derate mode engaged, limiting power output and hydraulic performance as a protective measure
• Intermittent loss of throttle control or unresponsive engine response to joystick commands
• Inability to access diagnostic menus or system parameters through the operator display

Potential Causes

The most common causes for Code 91-15 in used XCMG excavators include:

• Damaged or corroded CAN bus wiring harness, particularly at flex points near the cab pivot or engine bay where vibration and movement cause wear
• Loose or corroded connectors at the ECM, main controller, or junction points along the CAN network
• Failed termination resistors within the CAN bus network (typically 120-ohm resistors at each end)
• ECM or main controller failure, often due to moisture intrusion, voltage spikes, or component age
• Faulty ground connections affecting the communication circuit integrity
• Physical damage to wiring from rodents, maintenance work, or component replacement

How to Troubleshoot and Fix Code 91-15

Step 1: Visual Inspection Begin by thoroughly inspecting all CAN bus wiring from the ECM to the main controller. Focus on harness routing through high-wear areas—behind the cab, along the engine firewall, and near hydraulic lines. Look for chafed insulation, pinched wires, or evidence of previous repairs. On used excavators, check for brittle or cracked wire insulation common in machines with high hours.

Step 2: Connector and Ground Verification Disconnect and inspect all CAN bus connectors for corrosion, bent pins, or moisture. Clean connections with electrical contact cleaner and apply dielectric grease. Verify all ground points are tight, clean, and free from corrosion. Use a multimeter to test ground continuity (should read less than 1 ohm to chassis ground).

Step 3: CAN Bus Resistance Testing With the machine powered off and connectors separated, measure resistance between CAN-High and CAN-Low wires using a digital multimeter. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading significantly different indicates termination resistor failure or wiring issues.

Step 4: Voltage Testing With ignition on but engine off, measure voltage on CAN-High (should be approximately 2.5-3.5V) and CAN-Low (should be approximately 1.5-2.5V) relative to ground. Both signals should be present and stable. Fluctuating or absent voltages indicate controller or wiring problems.

Step 5: Advanced Diagnostics Connect XCMG-specific diagnostic software to check for additional communication fault details and verify both the ECM and main controller are responding. Monitor live CAN bus traffic to identify which component has failed to communicate.

Step 6: Component Replacement If wiring and connections test good, the issue likely resides in either the ECM or main controller. Check for available software updates before replacing hardware, as firmware issues occasionally cause communication errors.

Disclaimer: This guide provides general diagnostic information. Complex electrical issues should be addressed by qualified technicians with proper XCMG diagnostic equipment. Always consult the official service manual for your specific machine model and serial number range.