Kubota P1151 – Engine Control Module (ECM): Closed Loop High (LPG)

The engine's fuel control system has reached its maximum adjustment limit while operating in closed-loop mode on Liquefied Petroleum Gas (LPG). The Engine Control Module detects that the Closed Loop Base Multiplier (CL_BM) has exceeded the threshold (typically > 35% or < -35%) for a set number of updates, triggering a 'Power Derate 2' state.

• WG972
• WG1605
• WG1903
• WG2503
• WG3800
• Haulotte HA26 RTJ PRO
• Skyjack SJ61T
• Skyjack SJ66T

1. 1

   Check for any exhaust leaks upstream of or immediately near the HEGO (O2) sensor, as false air will skew sensor readings.

2. 2

   Verify that the LPG tank has adequate fuel, the service valve is fully open, and check for reduced fuel supply pressure.

3. 3

   Inspect the intake manifold, vacuum lines, and LPG fuel supply lines for any leaks.

4. 4

   Inspect the LPG Dual Stage Regulator (DSR) or Direct Electronic Pressure Regulator (DEPR) for freezing, coolant line integrity, or heavy oil buildup in the secondary chamber.

5. 5

   Monitor the HEGO sensor using a diagnostic tool to see if it is switching properly or if it is sluggish/non-responsive.

1. 1

   Visual & Audio Inspection

   Start the engine and listen/feel for exhaust leaks around the exhaust manifold gasket and the O2 sensor bung. Replace any blown exhaust gaskets.

2. 2

   Drain the Regulator

   Locate the LPG Dual Stage Regulator. Open the drain plug located at the bottom of the secondary chamber to drain any accumulated heavy oil/tar buildup that may be restricting fuel flow.

3. 3

   Check Connections

   Ensure the wiring harness connection on the electronic control section of the regulator (if equipped with a DEPR) is seated and locked.

4. 4

   Test/Replace the HEGO Sensor

   If no vacuum, fuel, or exhaust leaks are found and fuel pressure is within specification, the HEGO sensor is likely non-responsive. Remove the old O2 sensor and install a new OEM replacement.

5. 5

   Clear and Verify

   Use a Kubota diagnostic tool (or equivalent EControls software) to clear the P1151 fault code. Run the engine until it reaches operating temperature and enters closed-loop mode to verify the fuel trims stabilize and the code does not return.