Kobelco SK135SRLC-2 Fault Code R174: Complete Diagnostic Guide

What is Kobelco SK135SRLC-2 Fault Code R174?

Fault Code R174 indicates a communication error or malfunction in the engine control system's CAN bus network, specifically related to data transmission failures between the Engine Control Module (ECM) and other critical control systems. This code typically represents a break or degradation in the Controller Area Network communication protocol that allows the engine controller to interface with hydraulic, display, and monitoring systems.

In the Kobelco SK135SRLC-2 excavator, this fault is particularly critical because the CAN bus serves as the central nervous system for coordinating engine performance, hydraulic system responses, and operator interface functions. When communication fails, the machine may enter derate mode or experience reduced performance to prevent potential damage. For used excavators, this code often emerges from age-related wiring degradation rather than component failure.

Common Symptoms

• Warning lights on the instrument panel, particularly the engine diagnostic lamp or communication error indicator
• Intermittent loss of gauge functionality, including erratic fuel level, temperature, or hour meter readings
• Engine derate mode engagement, limiting RPM to 1500-1800 range regardless of throttle input
• Hydraulic system operating sluggishly or inconsistently due to ECM communication loss
• Complete failure to start or unexpected engine shutdown during operation

Potential Causes

The R174 fault code in used SK135SRLC-2 excavators typically stems from these common issues:

• Corroded or damaged CAN bus connectors, especially at the ECM harness connection points near the engine bay where moisture intrusion is common
• Worn or frayed wiring harness sections where cables rub against the boom cylinder or undercarriage frame—a known wear point on this model
• Failed termination resistors (120-ohm) at either end of the CAN network causing signal reflection issues
• ECM internal failure or corrupted firmware, though less common than wiring issues in used machines
• Loose or oxidized ground connections affecting the entire electrical system's integrity

How to Troubleshoot and Fix Code R174

Step 1: Visual Inspection of Harness and Connectors Begin by thoroughly inspecting the main engine wiring harness from the ECM to the cab. On used SK135SRLC-2 models, check the harness routing along the right side of the engine where it passes near the exhaust manifold—heat damage is common here. Disconnect the ECM connector (typically a 48-pin gray connector) and inspect pins for corrosion, bent contacts, or green oxidation. Clean with electrical contact cleaner and dielectric grease.

Step 2: Test CAN Bus Continuity and Resistance Using a digital multimeter, measure resistance between CAN-High and CAN-Low terminals at the ECM connector (refer to your service manual for specific pin locations—usually pins 23 and 24). You should read approximately 60 ohms with the key off, indicating proper termination resistors are present. If you read open circuit (OL) or significantly different values, trace the CAN bus wiring for breaks or disconnected termination resistors.

Step 3: Check Voltage and Ground Circuits With the key in the ON position (engine off), verify battery voltage (12-14V) is present at the ECM power supply pins. Test the ground circuit integrity by measuring voltage drop between the ECM ground pin and battery negative—readings above 0.2V indicate poor ground connections requiring cleaning and re-torquing.

Step 4: Diagnostic Software Scan Connect Kobelco-compatible diagnostic software (or a quality multi-brand scanner with J1939 protocol support) to read detailed fault data. Check for multiple simultaneous codes that might indicate a systemic electrical issue versus an isolated R174 fault. Clear codes after repairs and perform a dynamic test under load.

For used excavators specifically: Inspect harness protective loom for brittleness and replace sections showing UV damage or cracking. Check all chassis ground points for paint buildup or rust—sand clean and apply conductive grease before reconnecting.

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Disclaimer: This guide provides general diagnostic information for the Kobelco SK135SRLC-2. Always consult the official service manual for your specific machine serial number and year. If you're uncomfortable performing electrical diagnostics, consult a certified Kobelco technician to avoid potential ECM damage or safety hazards.