What is Kobelco SK75-8 Fault Code A255?

Fault Code A255 on the Kobelco SK75-8 excavator indicates a malfunction in the Engine Control Module (ECM) communication circuit or CAN bus system failure. This diagnostic trouble code (DTC) signals that the main controller has detected an interruption or degradation in the electronic communication network that connects the engine control unit to other critical systems including the hydraulic controller, instrument cluster, and monitoring systems.

The CAN (Controller Area Network) bus serves as the central nervous system for modern excavators, enabling real-time data exchange between multiple control modules. On the SK75-8, this network operates at specific voltage levels (typically 2.5V to 3.5V on CAN-High and 1.5V to 2.5V on CAN-Low lines). When this communication pathway fails, the machine loses coordinated operation between engine performance and hydraulic demand, severely compromising operational efficiency and safety systems.

Common Symptoms

• Warning lights illuminated: The engine check light and master warning indicator flash or remain solid on the instrument panel
• Erratic engine performance: Unexpected engine derating, rough idle, or inability to achieve full RPM under load
• Hydraulic system irregularities: Sluggish or unpredictable hydraulic responses due to loss of load-sensing communication
• Gauge cluster malfunctions: Digital displays freezing, incorrect readings, or complete gauge failure
• Machine entering limp mode: Reduced functionality with limited engine speed and hydraulic pressure as a protective measure

Potential Causes

Wiring harness damage is the primary culprit in used SK75-8 excavators, particularly where harnesses route near moving components or experience rubbing against the chassis near the engine compartment or undercarriage pivot points.

Corroded or loose connectors at the ECM, main harness junction boxes, or grounding points frequently develop resistance issues after years of exposure to moisture, dirt, and vibration.

ECM internal failure can occur in higher-hour machines, though this is less common than external wiring issues.

Voltage supply problems from a failing alternator, weak batteries, or poor ground connections disrupt CAN bus signal integrity.

Aftermarket component interference such as improperly installed radios, GPS units, or work lights can introduce electrical noise into the CAN network.

How to Troubleshoot and Fix Code A255

Step 1: Visual Inspection Begin with a thorough physical examination of all wiring harnesses from the ECM (located behind the operator cab near the engine firewall) to the main junction connector. Look specifically for abraded insulation, pinched wires near mounting brackets, or evidence of rodent damage. On used excavators, pay special attention to harness routing where the upper structure rotates—this is a known wear point on SK75-8 models.

Step 2: Test CAN Bus Voltage Using a digital multimeter with the ignition key in the ON position (engine not running), backprobe the CAN-High and CAN-Low wires at the ECM connector (typically pins identified in the service manual). You should measure approximately 2.5V differential between these lines. If readings are absent or significantly outside specification, check for 120-ohm terminating resistance across the CAN lines with the system powered off.

Step 3: Check Power and Ground Circuits Verify that the ECM receives proper voltage (typically 24V on Kobelco systems) at the power supply pin and that ground circuits show less than 0.5 ohms resistance to chassis ground. Corroded ground studs are extremely common on used machines operating in wet conditions.

Step 4: Connector Service Remove, inspect, and clean all connectors in the CAN network pathway using electrical contact cleaner. Apply dielectric grease to prevent future corrosion. Ensure connector locks are fully engaged—partial connections cause intermittent faults.

Step 5: Advanced Diagnostics If basic checks don't resolve the issue, utilize Kobelco diagnostic software (CAPS or equivalent dealer tool) to monitor real-time CAN bus traffic and identify which module is failing to communicate. This pinpoints whether the ECM itself or a downstream controller has failed.

For used excavators with this code, replacing components before thorough electrical testing often wastes money—harness repairs typically cost hundreds versus thousands for ECM replacement.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine serial number, and consider engaging a certified Kobelco technician for complex electrical diagnostics to avoid further damage to sensitive electronic components.