Case IH 1086-04 - UCM – UCM: Pneumatic trailer brake reservoir pressure sensor voltage low

This fault code indicates that the control module is receiving a voltage signal from the pneumatic trailer brake reservoir pressure sensor that has dropped below the acceptable minimum threshold. In a standard 5V reference sensor circuit, a voltage low condition typically points to a short to ground in the signal wire, an open circuit in the 5V supply wire, or an internal failure of the sensor itself.

• MAGNUM AFS Connect
• Magnum Series 250, 280, 310, 340, 380, 400 (including AFS Connect models)
• Optum Series 250, 270, 300, 340
• Puma Series 140, 150, 165, 175, 185
• Maxxum Series
• Vestrum Series
• Farmall Series

1. 1

   System Voltage Check: Verify that the tractor's battery voltage is healthy (above 11.5V - 12V). Low overall system voltage can sometimes trigger false voltage low sensor codes.

2. 2

   Visual Inspection: Locate the pressure sensor on the pneumatic trailer brake reservoir (air tank). Inspect the sensor's electrical connector and wiring harness for corrosion, moisture, backed-out pins, or physical damage.

3. 3

   Reference Voltage Test: Disconnect the sensor. Turn the key to the ON position. Use a multimeter to check the supply pin on the harness side for a 5V reference signal from the UCM. If 5V is missing, trace the harness back to the UCM to find the open circuit.

4. 4

   Short to Ground Test: Check the signal wire for continuity to ground. If it is shorted to ground, repair the wiring harness.

5. 5

   Sensor Verification: If the 5V reference is present, the ground is good, and the signal wire is not shorted, the sensor has failed internally and must be replaced.

1. 1

   Depressurize the System

   Turn off the tractor engine. Safely bleed all compressed air from the pneumatic trailer brake reservoirs to prevent injury when removing the sensor.

2. 2

   Disconnect

   Unplug the electrical connector from the faulty pressure sensor.

3. 3

   Remove Sensor

   Unscrew the sensor from the air reservoir or valve block port.

4. 4

   Install New Sensor

   Thread the new OEM sensor into the port. Ensure any required sealing washers or O-rings are in place to prevent air leaks. Tighten to the manufacturer's specified torque.

5. 5

   Reconnect

   Plug the electrical connector back into the new sensor, ensuring it clicks and locks securely.

6. 6

   Test

   Start the tractor and allow the air compressor to build system pressure. Spray a mild 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 diagnostic monitor or a service tool to clear the 1086-04 fault code from the UCM and verify it does not return.