New Holland DCU 19343 – DCU (Dosing Control Unit): Coolant control valve mechanically | mechanical defective blocked open | P20A3 Vent valve (Reductant Purge Control Valve) - short circuit high.

This code indicates an issue with the DEF (Diesel Exhaust Fluid) tank heater control valve (also known as the reductant purge control valve or coolant control valve). This valve is responsible for allowing hot engine coolant to circulate through the DEF tank to thaw frozen DEF in cold weather. The fault means the valve is either mechanically stuck in the open position or the electrical circuit controlling the valve is experiencing a "short circuit high" (short to battery voltage). When this valve is stuck open, hot coolant flows continuously, which can cause the DEF tank to overheat and trigger reduced engine power (derate).

• New Holland T7 Series (e.g., T7.170, T7.220, T7.235, T7.250, T7.260, T7.270)
• New Holland T8 Series
• New Holland T6 Series
• New Holland / Case Construction Wheel loaders
• New Holland / Case Construction excavators

1. 1

   Check Coolant Flow: Feel the coolant lines running to the DEF tank level/header unit. If the engine is warm but the ambient temperature is well above freezing, the lines should not be hot. If they are hot, the valve is stuck open and continuously flowing coolant.

2. 2

   Inspect Hose Routing: Verify that the coolant hoses were not installed backward during a previous repair. The heater control valve is a directional valve; if installed in the opposite direction, the valve cannot physically cut off the coolant flow, leading to continuous heating. (On some models, the DEF heater line with the red band must be connected to the top tube running to the front of the engine head).

3. 3

   Electrical Circuit Test: Inspect the wiring harness and the connector at the coolant control valve. Look for rubbed wires, melted insulation, or water intrusion that could cause a short circuit to battery voltage (Short Circuit High - P20A3).

4. 4

   Test the Valve: Use a multimeter to check the internal resistance of the valve solenoid. If it is shorted internally, the valve must be replaced.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical shorts. Allow the engine and coolant to cool down completely.

2. 2

   Locate the Valve

   Locate the DEF coolant control valve. It is typically spliced into the heater hoses running along the frame rail toward the DEF tank header.

3. 3

   Pinch Off Coolant Lines

   Use hose pinch-off pliers on both sides of the control valve to prevent excessive coolant loss.

4. 4

   Remove the Valve

   Disconnect the electrical connector from the valve. Loosen the hose clamps and pull the coolant hoses off the valve fittings.

5. 5

   Install the New Valve

   Install the replacement valve. Crucial Step: Ensure the valve is installed in the correct flow direction (usually indicated by an arrow on the valve body). If installed backward, it will not stop coolant flow.

6. 6

   Reassembly

   Secure the hose clamps and plug in the electrical connector. Remove the hose pinch-off pliers.

7. 7

   Refill and Bleed

   Top off the engine coolant as necessary. Start the engine and let it run, checking for coolant leaks around the new valve.

8. 8

   Clear Codes

   Use the CNH Electronic Service Tool (EST) to clear the DCU 19343 / P20A3 fault codes and verify that the DEF tank temperature normalizes.