Case IH 12658 – Vehicle Control Module (VCM / TECU) or Trailer Brake Control Module: Pneumatic output - delivery port - rear left - pressure dynamic error

This code indicates a dynamic pressure failure at the control/delivery port on the rear left of the pneumatic trailer brake valve. The system expects a specific pressure change (dynamic pressure) when the trailer brakes are commanded, but the pressure sensor is reading an implausible value, a delayed response, or no pressure change.

• Puma 130
• Puma 150
• Maxxum 135
• Magnum 235
• Magnum 310
• Optum

1. 1

   Start the tractor and allow the pneumatic system to build full pressure. Listen for audible air leaks around the rear left delivery port of the trailer brake valve and the gladhand connectors.

2. 2

   Locate the air brake pressure sensor on the pneumatic trailer brake valve. Disconnect the harness and inspect the pins for corrosion, moisture ingress, or pushed-back pins.

3. 3

   Use the CNH Electronic Service Tool (EST) to monitor the live data for the trailer brake pressure sensor. Depress the brake pedal and observe if the pressure reading changes smoothly. If the reading is stuck at zero or an implausible high value, the sensor is likely dead.

4. 4

   If the sensor reads correctly but the pressure is physically not reaching the port, check if the pneumatic trailer brake valve spool is sticking internally.

1. 1

   Relieve System Pressure

   Turn off the engine and repeatedly pump the brake pedal, or open the air tank drain lanyards until all pneumatic pressure is exhausted from the system.

2. 2

   Remove the Sensor

   Disconnect the electrical harness from the air brake pressure sensor. Using a wrench, carefully unscrew the pressure sensor (M12 x 1.5 thread) from the pneumatic trailer brake valve body.

3. 3

   Install New Sensor

   Thread the new pressure sensor into the port. Torque to the OEM specification (do not overtighten, as the brass/aluminum threads can strip).

4. 4

   Valve Replacement (If Applicable)

   If diagnostics point to a mechanical failure of the valve itself rather than the sensor, disconnect all pneumatic lines (mark them for reassembly) and remove the mounting bolts for the trailer brake valve assembly. Install the new valve and reconnect the lines.

5. 5

   Reassembly & Testing

   Reconnect the electrical harness. Start the tractor and allow the air compressor to fill the tanks to the cut-out pressure.

6. 6

   Leak Down Test

   Apply soapy water to the sensor threads and the rear left delivery port to ensure there are no leaks.

7. 7

   Clear Codes

   Connect the EST, clear fault code 12658, and test-drive the tractor with a trailer attached to verify proper braking operation.