Case IH 12504 – Vehicle Control Module (VCM) or Brake Control Module: Air pressure sensor (circuit 1) (rear axle) - short circuit to power supply

The controller is receiving a voltage signal from the rear axle's primary air pressure sensor that is abnormally high (typically equal to the 5V reference or 12V battery voltage). The system interprets this maximum voltage as a "short to power," which can be caused by a chafed wire touching a power source, a shorted connector, or an internal failure within the sensor itself.

• Case IH Puma
• Case IH Magnum
• Case IH Optum

1. 1

   Visually inspect the air pressure sensor on the rear axle pneumatic valve block and the wiring harness for chafing, pinched wires, or melted insulation.

2. 2

   Disconnect the sensor and check the connector pins for corrosion, water ingress, or bent terminals.

3. 3

   Perform a voltage test on the harness side with the key ON (engine off). Probe for 5V reference, ground, and signal. If the signal wire shows 5V or 12V while disconnected, trace and repair the harness short to power.

4. 4

   If harness voltages are correct (no voltage on the signal return wire when unplugged), the sensor has failed internally and must be replaced.

1. 1

   Depressurize the System

   Turn off the tractor. Chock the wheels. Drain the air from the pneumatic system by repeatedly pumping the brake pedals or opening the drain valve on the main air tank. Never remove a pneumatic sensor while the system is under pressure.

2. 2

   Disconnect Battery

   Disconnect the negative battery terminal to prevent electrical spikes.

3. 3

   Remove the Sensor

   Unplug the electrical connector from the faulty air pressure sensor on the rear axle circuit 1 block. Use a wrench to carefully unthread the sensor from the valve block or air line.

4. 4

   Install the New Sensor

   Apply a pneumatic-safe thread sealant to the threads of the new sensor (if it does not come with pre-applied sealant). Thread it into the port and tighten to the OEM torque specification (do not overtighten, as this can crack the brass fittings).

5. 5

   Reconnect

   Plug the electrical connector back into the sensor. Reconnect the battery.

6. 6

   Test

   Start the tractor and allow the air compressor to build system pressure. Spray a soapy water solution around the base of the new sensor to check for air leaks.

7. 7

   Clear Codes

   Cycle the key or use a CNH Electronic Service Tool (EST) to clear the inactive 12504 fault code.