What is Kobelco SK460-8 Fault Code P0628?

Fault Code P0628 on the Kobelco SK460-8 excavator indicates a "Fuel Pump Control Circuit Low" condition. This diagnostic trouble code (DTC) signals that the Engine Control Module (ECM) has detected an abnormally low voltage or current in the fuel pump control circuit, preventing proper fuel delivery regulation.

This code specifically affects the electronic fuel pump control system, which is critical for maintaining optimal fuel pressure throughout the engine's operating range. On the SK460-8's Hino J05E diesel engine, precise fuel delivery is essential for maintaining horsepower, meeting emissions standards, and preventing engine damage. When the ECM cannot properly command the fuel pump due to circuit issues, fuel pressure becomes erratic, leading to performance degradation and potential engine protection modes.

Common Symptoms

When P0628 is active on your Kobelco SK460-8, you may experience:

• Check Engine Light or malfunction indicator lamp (MIL) illuminated on the instrument panel
• Engine power derate or limited throttle response, especially under heavy load conditions
• Rough idle or unstable engine RPM when the machine is warming up
• Hard starting or extended cranking times, particularly in cold weather
• Black smoke from the exhaust due to incomplete combustion from improper fuel delivery

Potential Causes

The most common technical causes for P0628 on used SK460-8 excavators include:

• Damaged wiring harness or chafed wires in the fuel pump control circuit, especially near the engine mounting points where vibration causes conductor wear
• Corroded or loose electrical connectors at the fuel pump relay, ECM, or fuel pump module—common in machines operating in wet or corrosive environments
• Failed fuel pump relay or control module, which experiences contact degradation over time
• ECM internal driver circuit failure, though less common, can occur in high-hour machines
• Blown fuse in the fuel pump control circuit due to previous electrical faults or shorts
• Faulty fuel pump assembly with internal electrical faults causing low resistance readings

How to Troubleshoot and Fix Code P0628

Step 1: Visual Inspection and Connector Check Begin by thoroughly inspecting the fuel pump wiring harness from the ECM to the fuel pump assembly. On used excavators, focus on areas where the harness passes near the engine block, exhaust components, or frame members—these are common rub points. Check all electrical connectors for corrosion, bent pins, or moisture intrusion. Clean connectors with electrical contact cleaner and apply dielectric grease to prevent future corrosion.

Step 2: Electrical Testing with Multimeter Using a digital multimeter (DMM), test the fuel pump control circuit. With the key on and engine off, check for battery voltage (typically 24V on the SK460-8) at the fuel pump relay and pump connector. Test circuit resistance between the ECM connector pin (consult service manual for specific pin identification) and the fuel pump—readings should typically be below 5 ohms. Check for shorts to ground by measuring resistance between the control wire and chassis ground with the circuit disconnected (should read infinite resistance).

Step 3: Component Testing and Replacement Test the fuel pump relay by swapping it with an identical relay from another circuit (like the starter relay) to verify function. If available, use Kobelco's diagnostic software to monitor fuel pump command signals from the ECM in real-time. For used machines with high hours, inspect the fuel pump assembly for internal wear. Replace any components showing electrical faults, prioritizing harness repairs over part replacement when possible to reduce costs.

Disclaimer: This guide provides general diagnostic information. For complex electrical issues or if you're uncomfortable performing these tests, consult a certified Kobelco technician or heavy equipment mechanic. Improper diagnosis can lead to additional damage or safety hazards.