What is Kobelco SK250-6E Fault Code G-3?

Fault Code G-3 on the Kobelco SK250-6E indicates a main pump solenoid valve system malfunction, specifically related to abnormal electrical signal detection in the hydraulic pump control circuit. This code triggers when the excavator's electronic control unit (ECU) detects irregular voltage or resistance values from the proportional solenoid valve that regulates main pump displacement and hydraulic flow.

The SK250-6E uses an electronically controlled hydraulic system where the main pump solenoid valve modulates pump output based on operator inputs and load demands. When G-3 appears, the ECU has identified that the control signal sent to this valve doesn't match expected parameters, potentially causing the machine to enter a protective derate mode to prevent hydraulic system damage. This is particularly critical on this model because the main pump controls overall hydraulic power delivery—affecting swing, boom, arm, and travel functions simultaneously.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably slower cycle times on boom and arm operations
• Intermittent or complete loss of swing function while other hydraulics continue operating
• Error code displayed on the monitor panel with potential audible warning alarm
• Erratic pump response where hydraulic pressure fluctuates unpredictably during simultaneous multi-function operations
• Engine RPM fluctuation under load as the ECU attempts to compensate for hydraulic control irregularities

Potential Causes

The G-3 code typically stems from electrical or mechanical degradation common in used excavators:

• Solenoid valve coil failure due to internal winding deterioration from heat cycling and age
• Wiring harness damage at known rub points near the main pump mounting bracket where vibration causes insulation wear
• Corroded connector pins in the 8-pin main pump solenoid connector, particularly on machines operated in high-moisture environments
• ECU internal fault affecting the solenoid driver circuit (less common but possible on higher-hour units)
• Voltage supply issues from the machine's electrical system, including failing alternator or poor chassis grounds
• Contaminated hydraulic oil causing mechanical sticking of the solenoid valve spool

How to Troubleshoot and Fix Code G-3

Step 1: Visual Inspection and Connector Check Begin by accessing the main pump assembly on the right side of the engine. Disconnect the solenoid valve connector and thoroughly inspect all pins for corrosion, bent contacts, or moisture intrusion. On used SK250-6E excavators, this connector frequently shows green corrosion. Clean with electrical contact cleaner and dielectric grease.

Step 2: Electrical Testing with Multimeter With ignition off, measure solenoid coil resistance across the valve terminals—specifications call for 18-22 ohms at room temperature. Next, check supply voltage at the harness connector with ignition on; you should see 12-14V DC. Test harness continuity back to the ECU, checking for opens or shorts to ground along the entire length, especially where the harness passes near the swing motor.

Step 3: Functional Test and Component Replacement If resistance and voltage readings are within specification, perform a solenoid activation test using Kobelco's diagnostic software (or compatible aftermarket tools). Monitor current draw during activation—excessive current (above 2 amps) indicates internal valve sticking. For used machines, inspect the wiring harness routing for modifications or damage from previous repairs before replacing the solenoid valve assembly.

Step 4: Post-Repair Verification After replacing faulty components, clear stored codes using the diagnostic tool, and operate the machine through complete hydraulic cycles while monitoring for code recurrence.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual and consider professional diagnostics for complex electrical issues. Improper repairs may cause further damage or safety hazards.