Case IH 12818 – Trailer Brake Controller (TBC) or MTA CCM (Cab Control Module) / APH Stage V MR On-Board Diagnostics system: Failure of brake sensor 1 supply 'Short to Power'

The control module has detected an abnormally high voltage on the supply circuit for Brake Sensor 1. This typically means the sensor's wiring harness is shorted to a power source (such as battery voltage or a higher voltage reference line), or the sensor itself has failed internally.

• MAXXUM T4E
• Farmall 40
• Farmall 45
• Farmall 50
• Farmall 85A
• Farmall 95A
• Farmall 105A
• Farmall 115A
• Farmall 105U
• Farmall 110U
• Farmall 115U
• Maxxum 100
• Maxxum 110
• Maxxum 115
• Maxxum 120
• Maxxum 125
• Maxxum 130
• Maxxum 140
• Maxxum 150
• Puma series
• Magnum series
• Models with CVT or manual transmissions

1. 1

   Inspect the wiring harness leading to Brake Sensor 1 for chafing, melting, or pinched wires that could expose the copper to a 12V power source (diagnosing wiring short cause).

2. 2

   Disconnect the connector at Brake Sensor 1, turn the key to ON, and measure voltage at the supply pin on the harness side. If it reads 12V on a 5V reference line, the short is in the wiring harness (diagnosing wiring short cause).

3. 3

   If the harness voltage is correct, check the sensor's internal resistance to see if it has shorted internally (diagnosing internal sensor failure cause).

4. 4

   Clear the fault code using a diagnostic tool, cycle the key, and press the brake pedal to see if the code returns immediately (active short) or if it was a stored historical code.

1. 1

   Turn off the tractor, remove the key, and disconnect the negative battery cable to prevent electrical damage during repair.

2. 2

   Locate Brake Sensor 1. Depending on the model, this may be the pneumatic trailer brake pressure sensor on the air tank/valve assembly or the primary brake pedal switch in the cab.

3. 3

   If the diagnostic checks isolated the issue to the wiring harness, trace the wire back to the Trailer Brake Controller / Cab Control Module. Repair the shorted section of the wire using solder and heat shrink, or replace the affected harness section (e.g., Air Brake Sensor Wire Harness).

4. 4

   If the harness is intact and the sensor is internally shorted, remove the mounting hardware or unthread the faulty Brake Sensor 1.

5. 5

   Install the replacement sensor and torque to OEM specifications.

6. 6

   Reconnect the electrical harness, ensuring the connector clicks into place and is free of corrosion.

7. 7

   Reconnect the battery, turn the key on, and clear the fault codes. Test the braking system and trailer brake outputs to verify the repair.