Kubota P0123 – Engine Control Unit (ECU / ECM): TPS1 Signal Voltage High

The Engine Control Unit has detected that the Throttle Position Sensor 1 (TPS1) voltage is higher than 4.80 V for longer than 0.5 seconds. This indicates that the TPS circuit in the harness is shorted to power, there is an open sensor ground, or the sensor itself has malfunctioned.

• WG972
• WG1605
• WG1903
• WG2503
• G424FE
• Toro mowers
• Genie lifts (e.g., S-80, S-85)
• Crown forklifts

1. 1

   Check the 5.00 V Reference Feed (TPS POWER / 5 V_ext1) to verify it is not shorted to voltage.

2. 2

   Test the sensor ground circuit (5 Vrtn1) to ensure it is not open.

3. 3

   Ensure the TPS signal wire is not shorted to a voltage source.

4. 4

   Verify that all system ground connections are in place, clean, and secure.

5. 5

   Inspect the harness for physical damage, chafing, or loose connections at the throttle body connector.

1. 1

   Safety Preparation

   Park the machine on firm, level ground. Stop the engine, remove the key, and allow the engine to cool. Disconnect the battery's negative cable first to avoid accidental short circuits.

2. 2

   Wiring Repair / Replacement

   If your multimeter tests reveal an open ground or a short to power in the wiring, address the wiring issue. (Note: Official Kubota documentation states that "Kubota does not approve wire harness repairs," meaning if the harness is damaged, the official OEM repair is to replace the affected harness section).

3. 3

   Replace the Sensor / Throttle Body

   If the wiring, reference voltage, and grounds all test within specification, the Throttle Position Sensor itself is faulty. On many of these Kubota engines (like the WG1605), the TPS is integrated into the Electronic Throttle Body. You will need to remove the old throttle body assembly and bolt on the replacement.

4. 4

   Reassembly and Clearing Codes

   Reconnect the battery's negative cable. Turn the key on and use the Kubota Gasoline Service Tool (KGST) or a compatible OBD scanner to clear the DTCs. Start the engine to ensure the MIL remains off and the TPS voltage reads normally (below 4.80 V).