Case IH 12941 – Vehicle Controller / Trailer Brake Controller: Trailer Brake Control Line Pressure Higher Than Supply - Disagreement

A plausibility error where the system detects that the pressure in the trailer brake control line is reading higher than the system's supply pressure (exceeding it by more than 1 bar). This is physically impossible unless there is a trapped pressure issue, an internal valve bypass, or a faulty pressure sensor giving a skewed reading.

• MAXXUM T4E
• Maxxum 100
• Maxxum 110
• Maxxum 115
• Maxxum 125
• Maxxum 135
• Maxxum 145
• Maxxum 150
• MXU 115
• MXU 135
• Puma series
• Magnum series
• Farmall 115U

1. 1

   Connect the Electronic Service Tool (EST) and monitor live data for Supply Pressure and Control Line Pressure

2. 2

   Depressurize the trailer brake system completely and perform a sensor zero-state check (both sensors should read 0 bar)

3. 3

   Inspect the wiring harness to the TCV pressure sensors for chafing or corrosion that could cause high resistance

4. 4

   Perform a valve leak-down test to check for internal mechanical leaks in the Trailer Brake Valve and Park Brake Valve

1. 1

   Depressurize the System

   Safely bleed all air/hydraulic pressure from the tractor's trailer brake system.

2. 2

   Test/Replace the Sensor

   If your EST diagnostic check revealed that the Control Line Pressure sensor reads higher than 0 bar when the system is empty, locate the TCV pressure sensor on the trailer brake valve block. Disconnect the harness, unscrew the sensor, and replace it with a new unit.

3. 3

   Inspect the Trailer Brake Valve

   If the sensors read correctly at zero but the fault occurs dynamically during operation (e.g., when applying the park brake), the Trailer Brake Valve is likely failing internally.

4. 4

   Replace the Valve

   Disconnect the supply, pilot, and park brake tubes from the Trailer Brake Valve. Unbolt the valve assembly from its mounting bracket and install the replacement valve. Reconnect all pneumatic/hydraulic lines securely.

5. 5

   Clear and Calibrate

   Re-pressurize the system. Use the EST to clear fault code 12941. Actuate the service brakes and the park brake several times while monitoring the live data to ensure the Control Line Pressure never exceeds the Supply Pressure.