Case IH 19344 – DCU (Dosing Control Unit): Coolant control valve mechanically _mechanical defective blocked closed _P20A0 Vent valve (Reductant Purge Control Valve) -open circuit

The Dosing Control Unit (DCU) has detected an open electrical circuit or a mechanical blockage in the reductant purge control valve (DEF/AdBlue coolant control vent valve). If the AdBlue/DEF pressure exceeds 450 kPa and the cooling system valve is commanded open, the system expects the pressure to drop by at least 15 kPa within 2 seconds; failure to do so indicates the valve is mechanically stuck closed or electrically open.

• Tier 4a
• Case IH Magnum Series (180, 190, 210, 225, 235, 240, 250, 260, 290, 315, 340, 380 Series 4)
• Case IH Steiger Series (350, 400, 450, 500, 550, 600)
• Case IH Puma Series
• Case Construction Equipment CX Series Excavators (CX220E, CX260E)
• Case Construction Equipment Wheel Loaders

1. 1

   Check for Related Codes: Verify if other codes are present (such as P20A2 for short circuit low, P20A3 for short circuit high, or 3577 for DCU CAN errors). If multiple codes exist, diagnose electrical supply issues first.

2. 2

   Visual & Electrical Inspection: Inspect the wiring harness and connectors between the DCU and the Coolant Control Valve / Reductant Purge Control Valve. Look for chafed wires, corrosion, or disconnected pins that would cause an open circuit.

3. 3

   DCU Connection Check: Ensure all connectors at the Dosing Control Unit housing are properly seated and locked.

4. 4

   Functional Valve Check: Check if the coolant lines are warm leading to the DEF tank level unit. If the lines are cold when commanded open, the valve is mechanically stuck closed.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery to prevent electrical spikes while servicing the DEF/AdBlue system.

2. 2

   Repair Wiring

   If the diagnostic checks revealed a broken wire or corroded connector in the P20A0 circuit, repair the wiring harness and replace the damaged connector terminals.

3. 3

   Replace the Valve

   If the wiring is intact but the valve fails to actuate (mechanically stuck closed), drain the localized coolant/DEF lines, remove the defective Coolant Control Valve / Reductant Purge Control Valve, and install the replacement valve. Torque mounting bolts to OEM spec (typically 73 - 80 lb-ft for support brackets depending on the model).

4. 4

   Replace the DCU

   If the wiring and the valve both test perfectly fine, the open circuit is likely an internal failure within the DCU housing itself. You will need to replace the Dosing Control Unit.

5. 5

   Clear Codes and Test

   Reconnect the battery. Use an Electronic Service Tool (EST) to clear the DCU fault codes. Run the engine to normal operating temperature and verify that DEF pressure drops appropriately when the valve is commanded open.