Kubota P1154 – Engine Control Module (ECM) / Engine ECU: Closed Loop Low (NG)

The engine is operating in closed-loop fuel control mode on Natural Gas (NG), but the system is detecting a 'low' condition (typically meaning the fuel multiplier has dropped below a specific threshold, such as 35%, for a set number of updates). The engine is running lean or the system is unable to properly correct the air/fuel ratio, which illuminates the MIL and initiates a Power Derate 2 action.

• Kubota WG1605-E3
• WG-LSI series

1. 1

   Check for other DTCs: If any other fault codes are present, diagnose and repair those first, as they may be causing the P1154 code.

2. 2

   Inspect for Exhaust Leaks: Carefully check for exhaust leaks upstream of or immediately near the HEGO sensor.

3. 3

   Check Fuel Pressure: Measure the natural gas fuel supply pressure to the gaseous fuel control system to ensure it is not dropping below specification.

4. 4

   Inspect for Intake/Fuel Leaks: Check the intake manifold and fuel supply lines for any vacuum or fuel leaks.

5. 5

   Test the HEGO Sensor: Use a diagnostic scan tool to monitor the HEGO sensor voltage. Look for a non-responsive, flat-lined, or sluggish sensor.

1. 1

   Connect Diagnostic Tool

   Verify the P1154 code and check the live data for the HEGO sensor and fuel trims.

2. 2

   Exhaust System Repair

   Perform a visual and auditory inspection of the exhaust manifold and piping. If a leak is found before the O2 sensor, replace the compromised exhaust gaskets or piping.

3. 3

   Intake & Fuel System Repair

   Perform a leak check on the intake manifold and natural gas fuel lines. Fix any vacuum leaks by replacing intake gaskets or tightening loose fittings.

4. 4

   Regulator Adjustment/Replacement

   Connect a fuel pressure gauge to the NG fuel system. If the pressure regulator is delivering low pressure to the fuel control valve, adjust the regulator to OEM specifications. If it cannot hold pressure, replace the NG fuel pressure regulator.

5. 5

   Sensor Replacement

   If no mechanical leaks are found and fuel pressure is correct, but the HEGO sensor remains non-responsive on your scan tool, replace the HEGO sensor.

6. 6

   Verification

   Clear the fault codes and test-run the engine until it enters closed-loop mode to verify the repair was successful.