What is Kobelco SK75-8 Fault Code A015?

Fault Code A015 on the Kobelco SK75-8 excavator indicates a malfunction in the travel motor over-rotation system, specifically detecting abnormal rotation speed in one or both travel motors during operation. This code is triggered when the Electronic Control Unit (ECU) detects that a travel motor is rotating faster than the programmed parameters allow, which typically occurs when hydraulic flow exceeds normal operating conditions or when there's a loss of load-holding control.

This fault is critical for the SK75-8's performance because unchecked over-rotation can lead to loss of machine control during travel operations, potential hydraulic system damage, and premature wear on travel reduction gears. The Kobelco SK75-8 uses a closed-loop hydraulic system with precise electronic monitoring, making this fault code particularly important for maintaining safe operation on slopes or during high-speed travel modes.

Common Symptoms

When Code A015 is active on your SK75-8, operators typically experience:

• Erratic travel speed with one track moving noticeably faster than the other, causing the machine to veer or pull to one side
• Warning buzzer activation accompanied by the malfunction indicator lamp on the monitor panel
• Automatic travel speed deration, where the machine limits maximum travel speed to prevent further over-rotation
• Hydraulic whining or cavitation noises from the affected travel motor during operation
• Loss of straight-line tracking ability, requiring constant joystick correction to maintain direction

Potential Causes

The most common technical causes for A015 in used SK75-8 excavators include:

• Worn or damaged travel motor swashplate, allowing internal bypass and uncontrolled flow, especially common in machines with 5,000+ hours
• Faulty travel motor rotation sensor (speed pickup) providing incorrect signals to the ECU due to accumulated debris or magnetic sensor degradation
• Hydraulic control valve spool sticking in the main control valve, preventing proper flow regulation to the affected travel motor
• Damaged or corroded wiring harness at the travel motor connector, a known wear point on the SK75-8 where the harness flexes near the track frame pivot
• Low hydraulic oil level or contaminated hydraulic fluid causing inconsistent motor performance and speed fluctuations
• ECU calibration drift in older machines, where stored parameters no longer match actual component wear conditions

How to Troubleshoot and Fix Code A015

Step 1: Initial Diagnostic Check Connect a Kobelco-compatible diagnostic tool (Dr.EX or equivalent) to read live data from both travel motor sensors. Monitor rotation speeds while operating each track independently at 50% throttle. Compare left versus right motor RPM readings—a variance greater than 10% indicates the problematic side. For used excavators, this step often reveals sensor degradation before mechanical failure.

Step 2: Inspect Travel Motor Speed Sensors Physically examine the rotation sensor mounted on the suspect travel motor housing. Check the sensor air gap using a feeler gauge (specification: 0.5-1.0mm). Clean any metal debris from the magnetic pickup face using brake cleaner. Use a digital multimeter to measure sensor resistance (should read 800-1200 ohms). Inspect the three-wire harness from sensor to ECU, particularly where it routes along the track frame—this is a common rub-through point on used SK75-8s causing intermittent signals.

Step 3: Hydraulic System Verification Check hydraulic oil level at the sight glass and inspect for contamination or milky appearance indicating water intrusion. Measure hydraulic system pressure at the travel motor test port using a 5,000 PSI gauge (normal operating pressure: 3,300-3,600 PSI). Test the travel pilot pressure at the control valve (should be 28-32 bar). On older machines, worn valve spools can cause pressure inconsistencies.

Step 4: Travel Motor Internal Assessment If sensors and hydraulics check out, drain the travel motor case oil and inspect for metallic contamination indicating internal wear. Perform a travel motor leakage test by pressurizing ports and measuring bypass flow. Excessive internal leakage (more than 3 liters/minute at 350 bar) confirms swashplate or piston wear requiring motor rebuild or replacement.

Step 5: ECU and Wiring Final Check Inspect all ECU connections for corrosion, especially on machines stored outdoors. Check ground connections at the travel motor mounting bolts—poor grounding causes erratic sensor readings. Clear the code and test operate for 30 minutes under load. If code returns immediately, consider ECU reprogramming with updated Kobelco software to match component wear characteristics in high-hour machines.

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Disclaimer: This guide provides general troubleshooting information for the Kobelco SK75-8. Hydraulic systems operate under extreme pressure and require proper training and safety equipment. Always consult the official Kobelco service manual and consider professional diagnostic services for complex electrical or hydraulic repairs, especially when working with used equipment where maintenance history may be unknown.