Kubota P1155 – Engine Control Unit (ECU): Closed Loop Bank 1 High (Gasoline)

The engine is operating in closed-loop mode, and the Engine Control Unit (ECU) detects that the fuel trim (CL_BM) is less than -35%, meaning the system is attempting to pull a significant amount of fuel out of the mixture to correct a rich running condition or a fuel pressure anomaly. This is triggered by reduced fuel supply pressure, an injector that is stuck closed, or high fuel supply pressure. The ECU will initiate a 'Power Derate 2' to protect the engine.

• WG1605
• WG1903
• WG2503
• WG3800
• Haulotte HA16RTJ Pro
• Haulotte HA26 RTJ Pro
• Skyjack SJ63AJ
• Powerboss sweepers
• Multiquip generators
• Toro
• Vermeer
• Doosan

1. 1

   Check for concurrent codes using the Kubota Gasoline Service Tool (KGST), especially O2 sensor or fuel pressure codes

2. 2

   Check fuel supply pressure at the fuel rail and compare physical pressure against the Fuel Pressure Manifold Sensor (FPM) reading

3. 3

   Perform an injector balance test or manually inspect gasoline fuel injectors to identify if one is stuck closed

4. 4

   Verify that the HEGO (O2) sensor is responsive, as a lazy sensor can skew fuel trims

5. 5

   Inspect ECM grounds to ensure they are clean and tight, check vacuum hoses for kinks or leaks, and verify alternator output voltage is stable

1. 1

   Connect Diagnostics

   Hook up the KGST electronic diagnostic service tool to monitor live data, specifically focusing on fuel pressure, fuel trim (CL_BM), and O2 sensor voltage.

2. 2

   Inspect the Fuel Pressure Manifold

   The Kubota gasoline fuel system utilizes a Fuel Pressure Manifold assembly to regulate pressure. If fuel pressure is out of specification, test the Fuel Pressure Manifold Sensor (FPM) and the electric fuel pump.

3. 3

   Test/Replace Injectors

   If fuel pressure is normal, test the injectors. If an injector is found to be stuck closed (failing to click when manually pulsed), depressurize the fuel system and replace the faulty injector.

4. 4

   Replace Faulty Sensors

   If the FPM sensor is outputting out-of-range data causing the ECU to miscalculate fuel delivery, replace the sensor.

5. 5

   Re-flash ECU (If Applicable)

   For engines using wellhead gas (US/Canada), ensure the ECU software matches the fuel's calorific value. Re-flash using the KGST if necessary.

6. 6

   Verify Repair

   Clear the DTCs. Run the engine until it reaches operating temperature and enters Closed Loop mode. Monitor the fuel trims to ensure they stay above the -35% threshold.