New Holland TRANS 50 – Transmission Controller (TCU): Park Brake is powered off when in park

The park brake is spring-applied and hydraulically disengaged when 12V is applied to the park brake solenoid. Fault code TRANS 50 is logged when the transmission controller commands the power off to the Park relay (because the machine is shifted into the Park position), but the controller still senses 12V at the Park Brake coil. This indicates an electrical fault where power is reaching the solenoid when it shouldn't be.

• TG Series
• TG210
• TG230
• TG255
• TG285
• TJ Series
• T9000 Series
• T7 Series
• T8 Series
• T9 Series
• TM Series

1. 1

   Check the Park Brake Relay: Swap the park brake relay with a known good relay of the same type to see if the fault clears, as a stuck closed or internally shorted relay is the most common cause.

2. 2

   Inspect Wiring: Check the wiring harness between the transmission controller, the park brake relay, and the park brake solenoid for any areas where the wiring might be shorted to a 12V power source.

3. 3

   Check Fuses: Check the transmission controller and park brake fuses (often Fuse #39 on large articulated models). A shorted park brake solenoid can blow the fuse and cause the transmission controller to go offline.

1. 1

   Safely park the machine

   Safely park the machine on level ground and chock the wheels, as you will be working on the parking brake circuit.

2. 2

   Locate the power distribution box

   Locate the power distribution box / relay panel (often located behind the operator's seat or in the engine compartment, depending on the model).

3. 3

   Test the Park Brake Relay

   Identify the Park Brake Relay. Remove the relay and test it with a multimeter, or temporarily swap it with a known good relay.

4. 4

   Replace the relay if faulty

   If the relay is stuck closed, replace the relay. Clear the fault codes and test the machine's park brake operation.

5. 5

   Trace and repair wiring

   If the relay is good, use a multimeter to trace the wiring from the relay to the park brake solenoid on the transmission. Repair any chafed wires that are shorting to battery power.

6. 6

   Replace the park brake solenoid

   If the wiring is intact but the solenoid itself is internally shorted (which often blows the corresponding fuse), recover the hydraulic fluid if necessary, remove the defective park brake solenoid from the transmission valve block, and install a new solenoid.

7. 7

   Replace fuses and verify operation

   Replace any blown fuses, clear the fault codes, and verify that the transmission shifts normally and the park brake engages/disengages properly.