Case IH 3506 – Engine Control Unit (ECU) / Engine Control Module (ECM): Diagnostic fault check of synchronism for double potentiometer and Low idle switch (LIS)

This code indicates a plausibility error (lack of synchronism) between the accelerator pedal's dual potentiometers (APP1 and APP2) or between the potentiometer signal and the Low Idle Switch (LIS). The Engine Control Unit (ECU) has detected that the measured voltage of the accelerator pedal is out of the plausible range compared to the physical state of the idle switch.

• Case IH Axial-Flow Combines (e.g., 240 Series)
• Case IH / CNH Tier 4 Final Tractors and Loaders (e.g., N-Series TLBs)

1. 1

   Inspect the cabling and connection cables between the accelerator pedal (or hand throttle) and the ECU for chafing, damage, or loose pins.

2. 2

   Check the accelerator pedal sensor (double potentiometer) and the Low Idle Switch (LIS) for correct voltage output.

3. 3

   Verify if the accelerator pedal can detect full load and idle plausibility at least once without dropping the signal.

4. 4

   Check for a short circuit to ground or a short circuit to the supply voltage on the pedal signal circuit.

1. 1

   Inspect the harness

   Locate the wiring harness connecting the accelerator pedal/hand throttle to the ECU. Repair or replace the connection cable if any physical faults, corrosion, or shorts are found.

2. 2

   Test the sensor

   Using a multimeter or diagnostic tool, monitor the voltage of the accelerator pedal potentiometers and the state of the Low Idle Switch.

3. 3

   Replace the pedal/sensor

   If the wiring is intact but the voltage remains out of the plausible range (or the LIS fails to change state when the pedal is released), the accelerator pedal assembly or throttle position sensor must be replaced.

4. 4

   Recalibrate and clear

   After replacing the pedal or repairing the harness, turn the ignition on, clear the fault codes, and cycle the pedal to ensure the ECU registers full load and idle plausibility correctly.