Kobelco SK135SRLC-2 Fault Code B172: Technical Guide

What is Kobelco SK135SRLC-2 Fault Code B172?

Fault Code B172 indicates a malfunction in the track adjuster solenoid valve circuit or pressure sensor system within the hydraulic control module. This code specifically relates to the undercarriage tensioning system that maintains proper track tension on the Kobelco SK135SRLC-2 excavator.

The B172 code triggers when the Electronic Control Unit (ECU) detects an abnormal voltage signal, open circuit, or short circuit in the track adjuster solenoid valve wiring harness or sensor feedback loop. This system is critical because improper track tension directly affects machine stability, undercarriage component wear, and operational safety. On used excavators, this fault often stems from environmental exposure causing electrical degradation in the undercarriage area where moisture and debris accumulation is common.

Common Symptoms

When Code B172 is active, operators typically experience:

• Warning light illumination on the instrument cluster, often accompanied by a wrench or system malfunction icon
• Loss of automatic track tensioning capability, requiring manual adjustment procedures
• Intermittent electrical faults during startup or when operating on uneven terrain that flexes wiring harnesses
• Hydraulic pressure irregularities in the track tension circuit, potentially causing loose or overly tight tracks
• Stored fault codes in the ECM memory even after the immediate issue resolves temporarily

Potential Causes

The most common technical causes for Code B172 on used SK135SRLC-2 excavators include:

• Damaged or corroded wiring harness in the undercarriage area where cables route near moving track components
• Failed track adjuster solenoid valve due to internal coil degradation or contaminated hydraulic fluid causing valve sticking
• Pressure sensor failure or contaminated sensor port causing inaccurate feedback to the ECU
• Connector pin corrosion at the solenoid valve connection point, particularly common in machines operating in wet or coastal environments
• ECU ground circuit issues or poor chassis grounding points corroded over time
• Mechanical interference from track frame repairs or modifications that pinch or rub wiring insulation

How to Troubleshoot and Fix Code B172

Step 1: Visual Inspection and Connector Check Begin by thoroughly inspecting the track adjuster solenoid valve and its wiring harness located near the track frame assembly. On used excavators, look for abraded wire insulation, crushed conduit, or moisture intrusion at connector bodies. Disconnect the solenoid connector and inspect pins for corrosion, bent terminals, or contamination. Clean with electrical contact cleaner and dielectric grease.

Step 2: Electrical Testing with Multimeter Using a digital multimeter, perform resistance checks on the solenoid valve coil (typically 10-30 ohms depending on specifications). Test harness continuity from the ECU connector to the solenoid valve—any reading above 5 ohms indicates excessive resistance from corrosion or damaged conductors. Check for shorts to ground (should read infinite resistance/open circuit). Measure voltage supply at the solenoid connector with ignition on—should read battery voltage (12-14V).

Step 3: Pressure Sensor and Hydraulic System Verification Test the track adjuster pressure sensor output voltage using Kobelco diagnostic software or a scan tool capable of reading live data. Normal operating range is typically 0.5-4.5V depending on pressure. Inspect the sensor port for contamination or hydraulic fluid degradation. Check hydraulic pressure with a mechanical gauge (typical specification: 200-350 bar) to verify actual system performance versus sensor readings.

Step 4: Component Replacement and System Reset If testing reveals a faulty solenoid valve, replace it with OEM or equivalent parts, ensuring proper torque specifications on hydraulic fittings. For harness damage common in used machines, repair using proper gauge wire, heat-shrink connections, and protective conduit in wear-prone areas. After repairs, clear fault codes using diagnostic software and perform a functional test of the track tensioning system under load.

Critical Note for Used Excavators: Before replacing expensive components, thoroughly check for harness chafing points where cables contact the track frame during machine articulation—this is the most common failure point on aging SK135SRLC-2 models. Inspect all ground connections and clean corrosion from chassis ground points.

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Disclaimer: This guide provides general diagnostic information based on common technical issues. Hydraulic systems operate under extreme pressure and electrical diagnostics require proper equipment and training. Always consult the official Kobelco service manual for your specific machine serial number and seek professional assistance from certified technicians when performing complex repairs or working with pressurized hydraulic systems.