What is Kobelco SK135SR-2 Fault Code A035?

Fault Code A035 on the Kobelco SK135SR-2 excavator indicates a pilot pressure sensor circuit malfunction in the hydraulic system. This code specifically points to an electrical issue within the sensor that monitors hydraulic pilot pressure, which is critical for controlling the machine's joystick and pedal operations. The ECM (Engine Control Module) relies on this sensor data to ensure proper hydraulic flow and responsiveness during operation.

The pilot pressure sensor plays a vital role in the SK135SR-2's hydraulic control system by converting mechanical pressure into electrical signals that the controller can interpret. When this sensor circuit fails or sends abnormal readings, it directly affects the precision and safety of machine operation. This is particularly critical in Kobelco excavators, which use sophisticated proportional control technology to deliver smooth, responsive hydraulic functions. A malfunctioning pilot pressure sensor can compromise operator control and lead to erratic machine behavior.

Common Symptoms

• Intermittent or complete loss of joystick control, with hydraulic functions becoming unresponsive or sluggish
• Warning light illumination on the instrument panel, often accompanied by a buzzer alert
• Erratic hydraulic movement where attachments respond unpredictably to control inputs
• Reduced hydraulic power across all functions, as the ECM may enter a derate mode to protect the system
• Error code display on the digital monitor showing A035 specifically

Potential Causes

The most common technical causes for Code A035 on used SK135SR-2 excavators include:

• Damaged or corroded wiring harness connections at the pilot pressure sensor, particularly where the harness routes along the pilot valve assembly (a known wear point on this model)
• Failed pilot pressure sensor due to internal component degradation from heat cycling and vibration exposure
• Electrical short or open circuit in the sensor signal wire, often caused by harness rubbing against metal edges near the cab floor
• Corroded connector pins at the sensor plug, especially common in machines exposed to moisture or stored outdoors
• ECM internal fault affecting the sensor input circuit (less common but possible in high-hour machines)
• Low voltage supply to the sensor from damaged power supply wiring or poor ground connections

How to Troubleshoot and Fix Code A035

Step 1: Visual Inspection Begin by locating the pilot pressure sensor on the pilot valve block (typically mounted on the right side of the operator's seat). Inspect the sensor and its wiring harness for obvious damage, including frayed wires, cracked insulation, or corroded connectors. On used excavators, pay special attention to harness routing where it passes through the cab floor area—this is a common rub point on the SK135SR-2.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to check resistance across the sensor terminals. Kobelco specifications typically call for 200-400 ohms at room temperature (consult your service manual for exact values). Next, check for supply voltage at the harness connector—you should see approximately 5 volts on the power wire with the ignition on. Also verify ground continuity between the sensor ground wire and machine chassis (should read less than 1 ohm).

Step 3: Harness and Connector Service Inspect all connector pins for corrosion or bent terminals. Clean connections with electrical contact cleaner and apply dielectric grease. Trace the harness from sensor to ECM, checking for pinched or damaged sections. For used machines, consider securing loose harness sections with proper clamps to prevent future chafing.

Step 4: Sensor Replacement and Verification If testing reveals sensor failure, replace with a genuine Kobelco pilot pressure sensor (part numbers vary by production year—verify with your dealer). After installation, clear the fault code using Kobelco diagnostic software or by disconnecting the battery for 30 seconds. Test all hydraulic functions thoroughly before returning the machine to service.

Disclaimer: This guide provides general troubleshooting information. Hydraulic and electrical system repairs should be performed by qualified technicians with proper training and tools. Always consult the official Kobelco service manual for your specific machine serial number and follow all safety protocols when working on heavy equipment.