What is Kobelco SK130-8 Fault Code 6644?

Fault Code 6644 on the Kobelco SK130-8 excavator indicates a Main Relief Valve Solenoid Circuit Malfunction, specifically an open circuit or abnormal voltage condition in the hydraulic system's pressure control circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects improper electrical feedback from the main relief valve solenoid, which regulates maximum system hydraulic pressure.

This code is critical for the SK130-8 because the main relief valve directly controls peak hydraulic pressure throughout the entire hydraulic system. When the solenoid circuit fails, the excavator cannot properly modulate system pressure, potentially leading to reduced lifting capacity, sluggish hydraulic response, or complete loss of hydraulic functions. In used excavators, this fault often results from deteriorated wiring harnesses or corrosion in connectors exposed to years of harsh operating conditions.

Common Symptoms

• Hydraulic system derate mode – excavator operates at reduced power with limited boom/arm/bucket speed
• Illuminated malfunction warning lamp on the instrument cluster (typically amber or red hydraulic warning light)
• Erratic hydraulic performance – inconsistent cylinder speeds or intermittent loss of auxiliary hydraulic functions
• Audible relay clicking from the main control valve area when attempting hydraulic operations
• Error code displayed on the multi-information display with potential automatic shutdown in severe cases

Potential Causes

The most common technical causes for Code 6644 on used SK130-8 excavators include:

• Open circuit in solenoid wiring harness – frequently caused by wire chafing near the hydraulic pump mounting bracket where harness routing creates friction points
• Failed main relief valve solenoid coil – internal coil resistance outside specification range (typically 12-18 ohms for this model)
• Corroded or loose connector pins at the main control valve electrical connector (C-107), especially on machines operated in wet or coastal environments
• Damaged ECM driver circuit – less common but possible on high-hour machines with electrical system stress
• Intermittent ground fault in chassis grounding points G-203 or G-205 near the hydraulic pump assembly

How to Troubleshoot and Fix Code 6644

Step 1: Visual Harness Inspection Conduct a thorough physical inspection of the main relief valve solenoid wiring harness from the ECM to the hydraulic control valve. On used excavators, carefully examine areas where the harness passes near metal edges, especially the routing along the right-side frame rail and pump mounting points. Look for abraded insulation, pinched wires, or evidence of previous repairs using electrical tape.

Step 2: Electrical Testing with Multimeter Disconnect the main relief valve solenoid connector (located on the main control valve body). Using a quality digital multimeter, measure solenoid coil resistance – it should read between 12-18 ohms at room temperature. Next, check for continuity between each solenoid pin and chassis ground (should show infinite resistance/open circuit). Then verify supply voltage at the harness connector with ignition on – you should see battery voltage (12-14V) on the power supply pin.

Step 3: Connector and Ground Point Service Clean the electrical connector terminals using electrical contact cleaner and a small wire brush. Inspect connector pins for corrosion (green/white deposits) or pushed-back pins that create poor contact. Apply dielectric grease to prevent future moisture intrusion. Verify chassis ground points G-203 and G-205 are clean, tight, and free from paint or corrosion – these are critical for proper solenoid operation.

Step 4: Diagnostic Software Confirmation If available, connect Kobelco-specific diagnostic software (INSITE or equivalent dealer software) to perform active solenoid tests and monitor real-time voltage feedback. This helps differentiate between solenoid failure and ECM driver circuit issues. For used machines without service history, this step reveals previous fault patterns that indicate chronic harness problems versus component failure.

Step 5: Component Replacement Procedure If testing confirms solenoid failure, replacement requires draining hydraulic oil from the main control valve section. When replacing the relief valve solenoid assembly, always install a new O-ring seal and torque the retaining bolt to 18-22 Nm per factory specifications. After installation, clear fault codes and perform a hydraulic pressure test to verify proper system relief pressure (typically 34.3 MPa/4,975 PSI for the SK130-8).

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Kobelco service manual for your specific machine serial number. Hydraulic system work involves high pressures and potential safety hazards – if unfamiliar with these procedures, seek assistance from a certified Kobelco dealer or qualified heavy equipment technician.