New Holland DCU 19541 – DCU: Coolant control valve mechanically | Blocked closed | P20A1 Vent valve test plausibility test (startup)

During the startup or commissioning phase, the system runs a plausibility test on the DEF/AdBlue coolant control valve. The fault triggers when the system commands the valve to open but detects no corresponding pressure change or flow, indicating the valve is mechanically stuck closed or the line is blocked. This prevents the DEF system from being heated, eventually leading to frozen DEF and an engine derate.

• T6 series (T6.180)
• T7 series (T7.270)
• T8 series (T8.xxx)
• T9 series (T9.xxx)
• CR series (CR6.80, CR7.90, CR8.90, CR9.90)
• W170C
• W190C
• W230C
• LM series (LM6.32, LM7.35)
• Magnum
• Steiger
• Puma
• Maxxum

1. 1

   Visually inspect the DEF tank, supply module, and coolant lines for frozen fluid, debris, or physical blockages.

2. 2

   Verify the coolant lines to and from the DEF tank heater and supply module are not kinked, blocked, or installed incorrectly.

3. 3

   Remove the coolant control valve and test it mechanically by blowing through the inlet while holding the bottom port closed to see if it seals and opens correctly when actuated.

4. 4

   Inspect the wiring harness and connectors between the DCU and the coolant control valve for damaged pins, corrosion, or broken wires. Ensure the connector locks are fully seated.

5. 5

   Use the CNH Electronic Service Tool (EST) to run a 'Pressure Build Up Operation' or manually command the vent valve to open (e.g., 50% for 2 minutes) to verify if the valve actuates and pressure changes appropriately.

1. 1

   Park and secure machine

   Park the machine on a level surface, disengage all drives, engage the parking brake, lower all attachments, shut off the engine, and remove the key.

2. 2

   Cool down

   Allow the engine and exhaust components to cool completely to avoid burn injuries.

3. 3

   Manage coolant

   Drain a portion of the engine coolant or use hose pinch-off pliers on the coolant lines connected to the valve to prevent excessive fluid loss.

4. 4

   Disconnect wiring

   Disconnect the electrical wiring harness connector from the coolant control valve.

5. 5

   Disconnect lines

   Loosen the hose clamps and disconnect the coolant inlet line, coolant outlet line, and the bypass line from the valve.

6. 6

   Remove bolts

   Remove the retaining bolts (e.g., M14 or M6 bolts depending on the model) securing the coolant control valve and its support bracket.

7. 7

   Remove valve

   Remove the defective valve.

8. 8

   Install new valve

   Position the new DEF/AdBlue coolant control valve on the mounting support bracket and secure it with the retaining bolts (torque to OEM spec, e.g., 73-80 lb-ft for M14 bracket bolts).

9. 9

   Reconnect lines

   Reconnect the coolant inlet, outlet, and bypass lines, and tighten the hose clamps.

10. 10

    Reconnect wiring

    Reconnect the electrical wiring harness.

11. 11

    Refill coolant

    Refill the engine cooling system and bleed any trapped air.

12. 12

    Verify repair

    Connect the CNH EST diagnostic tool, clear the fault codes, and run a system test to verify the repair.