Case IH 520613-13 - ACM – ACM: Rear hitch position control sensor disagreement

The Failure Mode Identifier (FMI) '13' indicates an 'Out of Calibration' or 'Disagreement' condition. This fault is triggered when the control module detects that the signal voltage/resistance from the rear hitch position sensor (rockshaft potentiometer) does not match the expected parameters, or the sensor has lost its calibration values. It can also occur if the mechanical linkage to the sensor slips or freezes, causing the physical hitch position to disagree with the sensor's electrical feedback.

• MAGNUM AFS Connect
• Magnum AFS Connect series
• Magnum 400
• Puma series (130-240)
• Steiger series
• Maxxum/Farmall series

1. 1

   Inspect the physical linkage connecting the rotary potentiometer to the rear rockshaft to ensure the arm is not bent, frozen, or slipping on the sensor shaft.

2. 2

   Inspect the 3-pin weather-proof connector at the hitch position sensor for corrosion, pushed-out pins, or moisture intrusion.

3. 3

   Trace the wiring harness back to the ACM to check for chafing or shorts to ground/power.

4. 4

   Perform a sensor sweep test using a multimeter to verify the 5V reference signal and ground. Back-probe the signal wire and manually move the hitch or sensor arm to ensure the voltage/resistance sweeps smoothly without dropouts or dead spots.

5. 5

   Check if the system has simply lost its calibration memory (if the sensor tests good electrically and mechanically).

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical spikes during component replacement.

2. 2

   Remove the Faulty Sensor

   Disconnect the 3-pin wiring harness from the rear hitch position potentiometer. Unbolt the sensor bracket and carefully detach the mechanical linkage arm from the rockshaft.

3. 3

   Install the New Sensor

   Mount the replacement potentiometer and reconnect the mechanical linkage. Ensure the linkage has its required free play and is not binding at the top or bottom of the hitch stroke.

4. 4

   Reconnect Wiring

   Plug the 3-pin connector back into the sensor, ensuring the weather seal is seated properly.

5. 5

   Perform Hitch Calibration

   Enter the tractor's diagnostic menu via the AFS Pro monitor (or use the dealer electronic service tool) and run the 'Rear Hitch Calibration' procedure. This will command the hitch to fully raise and lower, saving the new potentiometer voltage limits to the ACM.

6. 6

   Clear Codes

   Clear the 520613-13 fault code from the ACM memory and test the hitch operation under load.