New Holland DCU 19337 – DCU: System frozen and not free in time | Defreezing Mode and Detection Errors (Back-flow line defreezing failed) | Reagent - backflow tube heating - open circuit.

The control module has detected an open circuit (a broken electrical connection or burned-out heating element) specifically in the DEF backflow (return) line, preventing the system from thawing the frozen return line within the required time limit.

• New Holland T7 Series (T7.220, T7.235, T7.250, T7.260, T7.270)
• New Holland T8 Series
• New Holland TS6
• New Holland Workmaster

1. 1

   Visually inspect the DEF backflow line (return hose from dosing module to tank) for physical damage, severe kinks, or broken wires near the connector.

2. 2

   Disconnect the electrical connector for the backflow line heater and inspect pins for corrosion, moisture, or pushed-out terminals.

3. 3

   Perform a resistance test with a multimeter on the DEF line side of the connector; an 'OL' (Open Loop) or infinite reading indicates a broken internal heating element.

4. 4

   Check the Line Heater Relay and main power supply fuses to the DCU to ensure the circuit receives voltage when commanded on.

1. 1

   Turn off the ignition and disconnect the machine's battery to prevent electrical shorts.

   Turn off the ignition and disconnect the machine's battery to prevent electrical shorts.

2. 2

   Clean the area around the DEF tank fittings and the DEF dosing pump to prevent dirt from entering the SCR system.

   Clean the area around the DEF tank fittings and the DEF dosing pump to prevent dirt from entering the SCR system.

3. 3

   Disconnect the electrical connector for the faulty DEF backflow line heater.

   Disconnect the electrical connector for the faulty DEF backflow line heater.

4. 4

   Disconnect the fluid fittings at both ends of the DEF backflow line (at the dosing unit and at the tank).

   Have a catch pan ready, and wash away any spilled DEF immediately with warm water, as it is highly corrosive to metal.

5. 5

   Unclip the old DEF line from its routing brackets and remove it from the machine.

   Unclip the old DEF line from its routing brackets and remove it from the machine.

6. 6

   Route the new heated DEF backflow line along the exact same path.

   Ensure it is secured in all factory clips to prevent chafing against the chassis or melting against hot exhaust components.

7. 7

   Snap the fluid fittings into place at the tank and dosing module until they click securely.

   Snap the fluid fittings into place at the tank and dosing module until they click securely.

8. 8

   Plug in the new line's electrical connector.

   Plug in the new line's electrical connector.

9. 9

   Reconnect the battery and verify the repair.

   Use a diagnostic scan tool to clear the DCU 19337 / P20B9 fault codes and run a DEF system leak/heater test to verify the repair.