Case IH 12822 – MTA CCM and APH: Trailer Brake Control Line Pressure Disagreement - Pressure High

The system detects a plausibility error where the actual pneumatic or hydraulic pressure on the trailer brake control line is reading too high compared to the commanded pressure.

• MAXXUM T4E
• Maxxum
• Vestrum
• Puma
• Magnum
• Farmall

1. 1

   Use a diagnostic lead to access the 'HH menu' on-board diagnostics to extract stored vehicle fault codes and confirm whether 12822 or 12976 is the primary active fault.

2. 2

   If diagnosing 12822 (Pressure Disagreement - High): Check the trailer brake control line for physical blockages.

3. 3

   If diagnosing 12822 (Pressure Disagreement - High): Inspect the Trailer Brake Control Valve (TCV) pressure sensor supply for a 'Short to Power' or 'Short to Ground'.

4. 4

   If diagnosing 12976 (Brake Demand Sensor Offset): Perform a plausibility check by comparing the output of the physical brake pedal switch (high/low state) against the demand pressure sensor output.

5. 5

   If diagnosing 12976 (Brake Demand Sensor Offset): Check the brake pedal demand sensor for an offset voltage when the pedal is completely released.

1. 1

   Access the Sensors

   Locate the brake pedal demand sensor (usually near the master cylinder/brake pedal assembly) and the trailer brake pressure sensor (located on the trailer brake control valve).

2. 2

   Inspect Wiring

   Check the wiring harnesses connecting the brake demand sensor and the trailer brake control valve to the CCM for chafing, shorts, or corrosion.

3. 3

   Test Sensor Output

   With the tractor stationary and the brake pedal released, monitor the sensor voltage. If the demand sensor is outputting a voltage indicating pressure when the pedal is at rest, the sensor has internally failed (offset failure).

4. 4

   Replace the Faulty Sensor

   Remove the defective brake demand sensor or pneumatic trailer brake pressure sensor and install the replacement part.

5. 5

   Clear and Calibrate

   Clear the fault codes from the CCM using the HH diagnostic menu. Perform a test drive, applying the brakes to ensure the plausibility check passes and the codes do not return.