Case IH 12502 – TECU (Tractor Electronic Control Unit) or Chassis Control Module: Air pressure sensor circuit 1 (rear axle) - open circuit or short to ground

Indicates a critical electrical failure in the monitoring circuit for the rear axle's air pressure system. The controller has detected that the voltage signal from "Circuit 1" of the rear axle air pressure sensor is either completely missing (open circuit) or has dropped to zero volts (short to ground).

• Puma 165
• Puma 180
• Puma 195
• Puma 200
• Puma 210
• Puma 215
• Puma 225
• Puma 230
• Magnum 250
• Magnum 280
• Magnum 310
• Magnum 380
• Magnum MX215
• Magnum MX245
• Magnum MX275
• Magnum MX305
• MXU 100
• MXU 110
• MXU 115
• MXU 125
• MXU 130
• MXU 135

1. 1

   Visually inspect the air pressure sensor on the rear axle and the wiring harness for chafing, cuts, or pinched wires against the chassis.

2. 2

   Disconnect the sensor plug and check for moisture, dirt, or corroded/bent pins inside the connector.

3. 3

   Turn the key to the ON position (engine off) and use a multimeter to check the sensor connector for a 5V reference signal from the TECU and a solid ground.

4. 4

   If the 5V reference is missing, test the continuity of the signal wire from the sensor harness back to the TECU to confirm if the wire is broken (open) or rubbing against the frame (shorted to ground).

1. 1

   Depressurize the System

   Park the tractor on a level surface, engage the parking brake, and turn off the engine. Safely bleed off all compressed air from the rear air tanks and trailer brake lines to prevent injury when removing the sensor.

2. 2

   Disconnect the Sensor

   Unplug the electrical harness connector from the faulty air pressure sensor.

3. 3

   Remove the Sensor

   Using an appropriately sized wrench, carefully unthread the sensor from the air tank or pneumatic line fitting.

4. 4

   Install the New Sensor

   Thread the new OEM sensor into the port. Ensure that the O-ring is seated properly or that the correct thread sealant is applied to prevent air leaks. Do not overtighten.

5. 5

   Reconnect

   Plug the electrical harness back into the new sensor until it clicks securely.

6. 6

   Test the System

   Start the tractor and allow the air compressor to build up system pressure. Spray a soapy water solution around the base of the new sensor to verify there are no air leaks.

7. 7

   Clear Codes

   Use the tractor's AFS display or an electronic diagnostic tool to clear the inactive 12502 fault code from the TECU.