Kubota P0122 – Engine Control Module (ECM): TPS1 Signal Voltage Low

The Engine Control Module (ECM) detects that the Throttle Position Sensor 1 (TPS1) signal voltage has dropped below 0.200 Volts for longer than 0.5 seconds. This is an emissions-related fault that will illuminate the Malfunction Indicator Lamp (MIL) and may cause an immediate engine shutdown or force the engine into a protective state.

• WG Series
• WG1605
• WG1903
• WG2503
• WG972
• Toro machines
• Crown Equipment forklifts
• Jacobsen mowers
• Genie lifts

1. 1

   Check the 5.00 V Reference Feed: Verify that the sensor is receiving its 5.00 V reference voltage. A loss of this feed will trigger the low voltage code.

2. 2

   Inspect the Signal Circuit: Check the TPS circuit in the wiring harness for an open circuit, damage, or a short to ground.

3. 3

   Check System Grounds: Ensure that all system ground connections are secure and in place. A poor ground connection can cause erratic or low voltage readings.

4. 4

   Inspect the Main ECM Connector: Check the main ECM connector to identify any blanked pins, loose connections, or corrosion.

1. 1

   Safety First

   Turn off the engine, relieve any system pressure, and ensure you are in a well-ventilated area.

2. 2

   Locate the TPS

   The Throttle Position Sensor is located within the Electronic Throttle Body assembly on the intake manifold.

3. 3

   Test the Wiring

   Using a multimeter, test the wiring harness leading to the throttle body for a short circuit to ground.

4. 4

   Repair Wiring (If Applicable)

   If the wiring harness is damaged, shorted, or the ground is loose, repair the wiring and/or connections to the sensor.

5. 5

   Replace the Throttle Body

   If the wiring, 5V reference, and grounds are all intact, the TPS itself has failed. Because the TPS utilizes a variable resistor and voltage divider circuit integrated directly into the Electronic Throttle Body, the entire throttle body assembly must be replaced.

6. 6

   Clear Codes

   Reconnect the battery/harness, use the Kubota Gasoline Service Tool (KGST) or a compatible diagnostic scanner to clear the DTC, and run the engine to verify the repair.