Kubota P0381 – Engine ECU: Glow heater relay driving circuit overheat

Triggers when the system detects a short circuit to battery voltage (+B) in the glow plug relay driving circuit or harness while the heater lamp is commanded on. Symptoms include faulty starting, an increase in white smoke, and the engine warning light turning ON.

• V3800-CR-TE4
• V3800-TIE4
• V3800-TIEF4
• V3800-TIEF4C
• Kubota M108X
• Baroness turf equipment
• Carrier diesel generator sets (e.g.
• RG2400)

1. 1

   Connect a computer to the engine ECU using Kubota's Diagmaster software and check the related signals on the Data Monitor screen to see if the 'Glow relay' data is functioning.

2. 2

   Bypass the temperature sensor to force the system to command the relay ON for testing by disconnecting the coolant temperature sensor and connecting a dummy resistor (15 to 25 kΩ) to simulate a temperature of –30 to –20 °C (–22 to –5 °F).

3. 3

   With the key switch OFF, unplug the ECU wiring harness connector and disconnect the glow relay. Measure resistance between the ECU wiring harness connector (terminals V18 / V38) and the glow relay to check for continuity and verify there is no short to battery voltage (+BP).

1. 1

   Turn key switch OFF

   Turn the key switch to the OFF position.

2. 2

   Disconnect components

   Disconnect the main connector from the Engine ECU and disconnect the glow relay from the harness.

3. 3

   Inspect wiring harness

   Inspect the wiring harness and connectors for physical damage, melting, or exposed wires causing a +B short circuit.

4. 4

   Replace wiring harness

   If the harness is damaged, it must be replaced. (Note: Kubota service manuals state that they do not approve of wire harness repairs, so a full harness replacement is the OEM-approved method).

5. 5

   Replace glow plug relay

   If the wiring harness tests normal (no shorts and good continuity), the glow plug relay itself has likely failed internally and must be replaced.

6. 6

   Verify repair

   Reconnect all components, remove any dummy resistors used for testing, and use the Diagmaster software to clear the DTC and verify the repair.