What is Kobelco SK200-8 Fault Code P0629?

Fault Code P0629 indicates a Fuel Pump "A" Control Circuit/Open condition in the Kobelco SK200-8 excavator's electronic control system. This diagnostic trouble code (DTC) means the Engine Control Module (ECM) has detected an abnormal electrical signal or open circuit in the fuel pump control circuit, preventing proper fuel delivery management.

In the SK200-8's Hino J05E engine, this code specifically relates to the fuel supply pump control solenoid circuit. The ECM continuously monitors voltage and resistance values to ensure the fuel pump operates correctly. When electrical continuity is lost or voltage falls outside specified parameters (typically 10-14 volts during operation), P0629 triggers. This is critical because improper fuel pump control directly affects injection timing, fuel pressure regulation, and overall engine performance—potentially causing immediate power loss or preventing startup entirely.

Common Symptoms

• Engine cranks but fails to start, or starts then immediately stalls
• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Significant power loss or derating, with the machine limiting RPM to protect the engine
• Rough idling or intermittent stalling during operation, especially under load
• Fuel pressure warning messages displayed on the monitor panel

Potential Causes

The most common technical causes for P0629 in used SK200-8 excavators include:

• Damaged or corroded wiring harness between the ECM and fuel pump relay/solenoid, particularly at connection points near the engine block where vibration causes wear
• Failed fuel pump control relay or solenoid valve, common in machines with 5,000+ operating hours
• Blown fuse in the fuel pump control circuit (typically 10-15A fuse in the main electrical panel)
• ECM connector corrosion at pins related to fuel pump control—check connector C141 specifically
• Open circuit or short to ground in the control wiring, often found where harnesses route over the engine or through bulkhead grommets
• Faulty ECM (less common but possible in used equipment with electrical history)

How to Troubleshoot and Fix Code P0629

Step 1: Visual Inspection Begin with a thorough visual inspection of the fuel pump wiring harness from the ECM to the fuel pump relay. Check for chafed wires, damaged insulation, or signs of rodent damage. Inspect all connector pins for corrosion, bent terminals, or moisture intrusion—particularly at the fuel pump relay connector and ECM connector C141. On used excavators, pay special attention to harness routing where cables contact metal edges or moving components.

Step 2: Electrical Testing Using a digital multimeter (DMM), verify the fuel pump relay operation. With the ignition in the ON position (engine off), check for battery voltage (12-14V) at the relay input terminal. Test relay coil resistance, which should typically read 80-120 ohms. Check continuity in the control circuit wiring from the ECM to the relay—resistance should be less than 5 ohms with no shorts to ground (infinite resistance to chassis ground).

Step 3: Component Testing and Replacement Check the fuel pump control fuse in the main fuse panel. If fuse integrity is confirmed, swap the fuel pump relay with an identical relay from another circuit (like the starter relay) to test if the relay is faulty. If the code persists after verifying wiring integrity, use Kobelco diagnostic software (or compatible J1939 scanner) to perform active testing of the fuel pump control circuit. Monitor live data for fuel pump command signals from the ECM. If all electrical checks pass but the code remains, the ECM fuel pump driver circuit may be damaged and require ECM replacement or professional repair.

Used Equipment Note: Before replacing expensive components like the ECM, always check for aftermarket wiring modifications, poorly executed repairs, or corroded grounds that are common in older machines. Clean all ground connections with electrical contact cleaner and dielectric grease.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine serial number and torque specifications. If you're unsure about electrical diagnostics, consult a certified Kobelco technician to prevent further damage to electronic components.