Kubota P1121 – Engine Control Module (ECM) / Engine Control Unit (ECU): FPP1/2 Simultaneous Voltages Out-of-Range

The computer detects that the voltage signals from both FPP1 and FPP2 have simultaneously fallen outside of their acceptable operating thresholds, causing the system to enter a Power Derate or Forced Idle mode.

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1. 1

   Visually inspect the physical accelerator pedal assembly for debris, dirt, or mechanical binding that might prevent the pedal from moving smoothly or returning to the rest position.

2. 2

   Inspect the wiring harness connecting the FPP sensor to the ECM for chafed wires, open circuits, or short circuits.

3. 3

   Check the FPP sensor connector pins for corrosion or moisture intrusion, which can skew the 5V reference signal.

4. 4

   Using a diagnostic scan tool, monitor the live voltage data for FPP1 and FPP2 with the key ON and engine OFF. Slowly depress the pedal from 0% to 100%. Both voltages should sweep smoothly without dropping out, spiking, or flatlining.

1. 1

   Disconnect Power

   Turn the key off and disconnect the battery before servicing electrical components to prevent short circuits.

2. 2

   Clean and Secure Connections

   Disconnect the FPP sensor harness. Clean the terminals with electrical contact cleaner and ensure the connector seats firmly. Re-test the machine.

3. 3

   Repair Harness

   If continuity tests reveal a short or break in the signal, 5V reference, or ground wires between the pedal and the ECM, repair the damaged section of the harness.

4. 4

   Replace the FPP Sensor

   If the wiring is intact but the FPP1/FPP2 voltages remain out of range or erratic during the sweep test, remove the mounting bolts securing the accelerator pedal assembly to the floorboard, disconnect the electrical pigtail, and install a new pedal assembly.

5. 5

   Clear Codes

   Reconnect the battery, clear the P1121 fault code using a diagnostic tool, and test drive the machine to verify throttle response is restored and the code does not return.