John Deere 000029.03 – ECU: Hand Throttle Signal Voltage High

The Engine Control Unit (ECU) has detected that the signal voltage from the hand throttle potentiometer is above the expected maximum specification. This indicates a shorted circuit or a faulty sensor, which disrupts the signal being sent from the hand throttle to the ECU regarding the desired engine speed.

• 5045E
• 5050E
• 5055E
• 5058E
• 5060E
• 5065E
• 5067E
• 5075E
• 5085E
• 5090E
• 5100E
• 5065M
• 5075M
• 5085M
• 5090M
• 5095M
• 5100M
• 5105M
• 5115M
• 5120M
• 5125M
• 5130M
• 5080R
• 5090R
• 5100R
• 6100E
• 6110E
• 6115E
• 6120E
• 6090M
• 6100M
• 6110M
• 6R Series Tractors
• 7R Series Tractors
• 8R Series Tractors
• 9660 STS
• 9760 STS
• 310G Backhoe
• 7420 tractor

1. 1

   Ensure both the hand and foot throttles are fully returned to the idle position before starting the engine (operator presence check)

2. 2

   Visually inspect the wiring harness and connectors between the hand throttle sensor and the control unit for pinched, chafed, or corroded wires and loose connections

3. 3

   Check for moisture in the ECU and foot pedal connectors; clean with electronic contact cleaner if necessary

4. 4

   Check fuses (e.g., F24) to ensure a blown fuse isn't causing a missing ECU message

5. 5

   Review other active fault codes (e.g., ACU 001079.03, ACU 001080.03) that might indicate a broader sensor supply voltage issue

1. 1

   Test potentiometer resistance

   Disconnect the sensor and measure resistance (Ohms) across the outer terminals. Then, move one probe to the center (wiper) terminal and slowly sweep the throttle from minimum to maximum. The resistance should change smoothly without sudden jumps or dropouts.

2. 2

   Perform voltage test

   With the sensor connected and key 'ON', back-probe the signal wire. Sweep the throttle lever; voltage should increase smoothly (typically 0.5V at idle to 4.5V at full throttle). A voltage stuck high indicates a sensor or wiring issue.

3. 3

   Check wiring harness

   Test for continuity on the signal, power, and ground wires. Inspect specifically for a short circuit where the signal wire may be contacting a power source, causing the high voltage reading.

4. 4

   Replace hand throttle sensor

   If the potentiometer fails the resistance or voltage tests, replace the hand throttle sensor assembly.

5. 5

   Calibrate new sensor

   Perform a calibration procedure using the onboard display or a diagnostic tool to teach the control unit the voltage range of the new sensor. On some models, manual setting of idle and full-throttle voltages may be required first.