Case IH F82 – Transmission Controller / ECU: Foot Throttle Position Sensor Potentiometer Short Circuit To +8 Volts Or +12 Volts

The system detects an abnormally high voltage on the foot throttle sensor circuit, indicating a short to a power source. The primary symptom of this fault is that the transmission will not upshift during engine braking while the tractor is in transport auto-shift mode.

• MXM
• MXM 120
• MXM 130
• MXM 135
• MXM 140
• MXM 150
• MXM 155
• MXM 165
• MXM 175
• MXM 180
• MXM 190
• TM115
• TM165

1. 1

   Turn the Key OFF, then turn the Key ON.

2. 2

   Enter Diagnostic Mode on the instrument cluster.

3. 3

   Navigate to menu H9, channel 6 (Accelerator Pedal volts).

4. 4

   Operate the accelerator pedal. A properly functioning pedal should read approximately 20% when released and 55% when fully depressed.

5. 5

   Check if the value continuously reads greater than 55% while operating the pedal, which confirms the short circuit.

6. 6

   Disconnect the accelerator potentiometer connector (C256) and the processor connector (C239).

7. 7

   Inspect the connectors for debris, water ingress, or damaged pins.

1. 1

   Safety First

   Stop the engine, let it cool, and ensure the machine is parked safely. Do not start the engine during the electrical service procedures.

2. 2

   Harness Inspection

   With connectors C256 and C239 disconnected, use a multimeter to test the wiring harness between the foot throttle potentiometer and the controller.

3. 3

   Locate the Short

   Test the signal wire for continuity to the +8V or +12V power supply wires.

4. 4

   Repair Wiring

   If a short circuit is found in the harness (often caused by chafing against the chassis or degraded insulation), repair or replace the damaged section of the wiring harness.

5. 5

   Replace Sensor

   If the wiring harness tests perfectly fine, the short circuit is likely internal to the potentiometer itself. Remove the faulty foot throttle potentiometer and install a new one.

6. 6

   Recalibrate/Verify

   Reconnect all harnesses, turn the key ON, enter Diagnostic Mode (H9, channel 6), and verify the pedal now sweeps smoothly from 20% to 55% without exceeding the upper voltage threshold. Clear the fault codes.