Case IH 12657: Pneumatic output - delivery port - rear left - pressure sensor electrical error

The control system has detected an electrical fault (such as an open circuit, short circuit, or out-of-range voltage) in the pressure sensor circuit that monitors the pneumatic output delivery port on the rear left of the machine.

• Puma
• Optum
• Magnum
• Maxxum
• Vestrum
• Farmall
• T5
• T6
• T7
• T8

1. 1

   Locate the pneumatic trailer brake pressure sensor at the rear left delivery port of the tractor's air brake system.

2. 2

   Inspect the sensor's electrical connector for water ingress, corrosion, or backed-out pins.

3. 3

   Check the wiring harness leading from the sensor to the ECU for chafing, breaks, or short circuits.

4. 4

   Verify that the sensor is receiving the correct reference voltage and ground from the control module.

5. 5

   Ensure there are no severe air leaks at the rear left port that could cause erratic sensor behavior, though the primary focus should be on the electrical circuit.

1. 1

   Turn off the tractor and relieve all compressed air from the pneumatic trailer brake circuit to prevent injury.

2. 2

   Disconnect the electrical harness from the rear left pneumatic pressure sensor.

3. 3

   Unscrew the faulty pressure sensor from the delivery port.

   Note: the sensor thread is typically M12 x 1.5

4. 4

   Install the new OEM pressure sensor and tighten it to the manufacturer's specified torque.

5. 5

   Reconnect the electrical harness.

6. 6

   Start the tractor, allow the air compressor to build up pneumatic pressure, and test the trailer brake system for leaks and proper operation.

7. 7

   Use a diagnostic tool to clear fault code 12657 from the system.