Kubota P0629 – Engine Control Unit (ECU): Fuel Pump Relay Coil Short-To-Power / SCV drive system abnormality B + short

The control module detects that the voltage on the SCV or fuel pump relay control circuit is higher than expected (shorted to battery voltage) for a continuous duration (typically 0.7 to 2.6 seconds) while the key is ON and battery voltage is normal. This forces the engine into a derated state (output limited to approximately 50%), limits speed, worsens exhaust emissions, and may force the engine to stop entirely.

• V3800
• V3307
• V6108
• M108X
• M108S
• SVL75
• Baroness mowers
• Carrier units

1. 1

   Verify battery voltage is normal (typically under 16.0 volts)

2. 2

   Visually inspect the wiring harness between the ECU and the SCV (or fuel pump relay) for rubbed, melted, or broken wires that could cause a short to battery voltage (+B)

3. 3

   Inspect the ground straps at the ECU and the fuel pump module for corrosion or loose connections

4. 4

   Measure the resistance of the fuel pump relay coil or the SCV coil to check for an internal short in the relay pull-in coil

5. 5

   Inspect the Controller Area Network (CAN) bus communication lines for shorts or poor electrical connections

1. 1

   Power Down

   Turn the key switch to the 'OFF' position to unlatch the code and ensure the system is safe to work on.

2. 2

   Access the Component

   Locate the fuel pump relay (often under the dash or in the engine fuse box) or the Suction Control Valve (mounted directly on the HP3 high-pressure fuel supply pump).

3. 3

   Isolate the Short

   Disconnect the SCV or fuel pump relay from the harness. Use a multimeter to test the harness side for voltage. If battery voltage is present on the control wire when it shouldn't be, trace the harness back to the ECU and repair the shorted wire.

4. 4

   Replace the Faulty Component

   If the wiring harness tests fine, the short is likely internal to the component. Replace the fuel pump relay or the Suction Control Valve.

5. 5

   Reassemble and Clear Codes

   Reconnect all harnesses, clear the DTCs using a diagnostic scanner or Kubota Diagmaster, and run the engine to verify that full power is restored and the code does not return.