What is Kobelco SK135SRLC-2 Fault Code A255?

Fault Code A255 on the Kobelco SK135SRLC-2 excavator indicates a malfunction in the Engine Control Module (ECM) communication circuit or a data link error between the engine controller and the machine's main monitoring system. This diagnostic trouble code (DTC) specifically relates to a breakdown in the Controller Area Network (CAN) bus communication, which allows the engine ECM to share critical operational data with the machine's display panel and other electronic control units.

This fault is particularly critical for the SK135SRLC-2 because the CAN bus system manages engine parameters, hydraulic load sensing, and operator interface functions. When communication fails, the machine cannot properly regulate engine performance, monitor operating temperatures, or display accurate diagnostic information. For used excavators, this code often signals deteriorating wiring harnesses or corroded connectors rather than actual ECM failure.

Common Symptoms

When Code A255 is active, operators typically experience:

• Complete loss of engine data on the instrument panel (RPM, coolant temperature, fuel level showing dashes or zeros)
• Illuminated malfunction warning lamp or check engine light on the dashboard
• Intermittent engine derate or unexpected power reduction during operation
• Inability to access diagnostic information through the standard display screen
• Erratic gauge behavior where readings fluctuate wildly or freeze completely

Potential Causes

The most common technical failures triggering A255 on used SK135SRLC-2 excavators include:

• Damaged CAN bus wiring harness at known rub points near the engine mount brackets or undercarriage routing paths
• Corroded or moisture-infiltrated connectors at the ECM interface, particularly the 38-pin main harness connector
• Failed termination resistors within the CAN network (typically 120-ohm resistors at each network endpoint)
• ECM internal communication module failure, though less common than wiring issues
• Voltage supply problems to the ECM from the main power relay or chassis ground connections
• Aftermarket component interference from non-OEM radios, GPS trackers, or monitoring devices tapping into the electrical system

How to Troubleshoot and Fix Code A255

Step 1: Visual Inspection of Wiring and Connectors Begin by thoroughly examining the engine harness from the ECM forward to the bulkhead connector. On used machines, focus on areas where the harness contacts the frame or passes near moving components. Look for abraded insulation, pinched wires, or green corrosion on terminals. Disconnect the main ECM connector and inspect for bent pins, moisture, or oil contamination.

Step 2: Test CAN Bus Integrity Using a digital multimeter, measure resistance between the CAN-High and CAN-Low wires at the ECM connector with the key off and all modules disconnected. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one missing terminator; infinite resistance suggests an open circuit in the network wiring.

Step 3: Verify ECM Power and Ground Circuits Check that the ECM receives proper battery voltage (12-14 VDC) at the power supply pins with the key on. Measure ground circuit resistance from the ECM ground pins to battery negative—it should be less than 0.5 ohms. Clean and tighten all ground connections, especially chassis ground points that corrode on older machines.

Step 4: Software Diagnostics and Component Isolation Connect Kobelco-specific diagnostic software (EPOS or compatible tool) to retrieve freeze frame data and monitor live CAN bus activity. If communication remains absent, temporarily disconnect aftermarket accessories to rule out network interference. For persistent failures after wiring verification, ECM replacement may be necessary, but ensure proper programming and component registration to the machine serial number.

Critical Note for Used Excavators: Before replacing the ECM (a costly repair), always inspect connector terminals for "fretting corrosion"—a common issue where micro-movements create oxidation on contact surfaces. Cleaning terminals with electrical contact cleaner and applying dielectric grease often resolves intermittent A255 codes without parts replacement.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Kobelco service manual for your specific machine serial number and perform diagnostics according to manufacturer procedures. If unfamiliar with high-voltage electrical systems or CAN bus networks, seek assistance from a certified Kobelco service technician.