Case IH 19343 – DCU: Coolant control valve mechanically defective blocked open | Vent valve (Reductant Purge Control Valve) - short circuit high

The system has detected that the DEF tank's coolant heater control valve is mechanically stuck in the open position, or its electrical circuit is shorted to a high-voltage source. This causes hot engine coolant to flow continuously through the DEF tank heating loop, potentially overheating the DEF fluid and damaging components.

• Tier 4a
• Magnum series (235-340 Series 4)
• Steiger series (350-600)
• Quadtrac / Rowtrac
• Puma series
• Farmall Tier 4B models
• CX-E Series (CX170E, CX220E, CX260E)

1. 1

   Perform a physical temperature check by feeling the coolant lines going to the DEF tank level unit. If the lines are hot when the system should be off, the valve is confirmed to be stuck open.

2. 2

   Verify hose routing to ensure the DEF tank hoses are installed correctly. The DEF heater line with the red band must be connected to the top tube running to the front part of the engine head. Reversed hoses cause continuous hot water circulation.

3. 3

   Inspect the wiring harness leading to the Reductant Purge Control Valve for chafed wires or melted insulation that could be causing a short circuit high (short to battery voltage).

4. 4

   Clear the fault code and operate the machine to test for an intermittent sticking valve. If the fault returns repeatedly, the valve must be replaced.

1. 1

   Turn off machine and disconnect battery

   Turn off the machine, allow the engine to cool completely, and disconnect the battery to prevent electrical shorts.

2. 2

   Drain engine coolant

   Drain a portion of the engine coolant to prevent excessive spillage when disconnecting the valve lines.

3. 3

   Locate DEF Coolant Control Valve

   Locate the DEF Coolant Control Valve (typically an inline 12V valve connected to 5/8" coolant hoses routing to the DEF tank).

4. 4

   Disconnect electrical connector

   Disconnect the electrical connector from the valve.

5. 5

   Remove retaining bolts

   Remove the retaining bolts securing the coolant control valve support bracket (e.g., M14 bolts on Farmall/Magnum models).

6. 6

   Disconnect coolant hoses and remove valve

   Disconnect the coolant hoses from the valve and remove the defective unit.

7. 7

   Install new valve

   Install the new coolant control valve assembly onto the support bracket. Torque the retaining bolts to OEM specifications (e.g., 73 - 80 lb-ft / 99 - 108 N·m for standard M14 bracket bolts).

8. 8

   Reconnect coolant hoses

   Reconnect the coolant hoses, ensuring the supply and return lines are not reversed.

9. 9

   Reconnect electrical connector

   Reconnect the electrical connector.

10. 10

    Refill engine coolant

    Refill the engine coolant to the specified level.

11. 11

    Reconnect battery and clear codes

    Reconnect the battery, use a diagnostic tool to clear the DCU fault codes, and run the machine to verify the DEF tank is no longer overheating.