Deutz-Fahr M138 – Engine ECU (EMR - Electronic Engine Regulation): Hand Throttle Sensor - Short circuit to +12V

The signal voltage from the hand throttle potentiometer is implausibly high, registering a short circuit to a +12V power source. The controller detects that the signal is out of its normal operating range and is implausible compared to the idle sensor or foot throttle.

• Deutz-Fahr Series 5 (5100, 5110, 5120, 5C, 5D, 5G)
• Deutz-Fahr Agrotron Series (K, M, and 6 series)
• SAME Virtus J
• Nitro R

1. 1

   Inspect the wiring harness running from the hand throttle lever in the right-hand cab console to the Engine ECU for chafed insulation that might be shorting the signal wire to a +12V power wire.

2. 2

   Disconnect the hand throttle potentiometer and check the connector pins for corrosion, moisture, or bent terminals that could bridge the 12V reference to the signal pin.

3. 3

   With the sensor disconnected, turn the key to the ON position. If the fault code changes from M138 FMI 3 (Short to +12V) to M138 FMI 4 (Short to Ground / Open Circuit), the wiring is likely intact, and the potentiometer itself has an internal short.

4. 4

   Use the SERDIA or EDS (Electronic Diagnosis System) tool to monitor the live voltage of the hand throttle sensor. If the voltage is pegged at maximum regardless of lever position, the sensor is faulty.

1. 1

   Power Down

   Turn off the tractor ignition and disconnect the negative battery terminal to prevent electrical spikes.

2. 2

   Access the Sensor

   Remove the trim panels on the right-hand operator console to access the base of the hand throttle lever assembly.

3. 3

   Remove the Faulty Sensor

   Disconnect the electrical plug from the hand throttle potentiometer. Remove the mounting screws or bolts securing the potentiometer to the mechanical lever linkage.

4. 4

   Install the New Sensor

   Mount the replacement potentiometer, ensuring the mechanical linkage aligns correctly with the sensor's rotary sweep. Secure the mounting hardware.

5. 5

   Reconnect

   Plug the electrical connector back into the sensor and reconnect the battery.

6. 6

   Clear Codes and Calibrate

   Turn the ignition ON. Use the tractor's infocenter display or the EDS/SERDIA diagnostic tool to clear the inactive M138 fault code. Cycle the hand throttle through its full range of motion to ensure the ECU registers the correct minimum and maximum values.