Case IH 19084 – DCU (Dosing Control Unit): Voltage supply 3 - Coolant control valve and reverting valve (UB3) electrical | Short circuit to Ground UB3 | P20A2 Vent valve (Reductant Purge Control Valve) - short circuit low

The Dosing Control Unit (DCU) has detected a short circuit to ground on the UB3 voltage supply circuit. This specific circuit provides 12V power to the Coolant Control Valve (which regulates engine coolant flow to heat the DEF/AdBlue tank) and the Reverting Valve / Vent Valve (which purges the reductant lines). Because the circuit is shorted to ground, the voltage is pulled low (triggering the associated OBD code P20A2), preventing the DEF system from properly heating the tank or purging the lines.

• Tier 4a
• Case IH Magnum Tractors: 235, 255, 285, 315, 340 (Series 4)
• Case IH Steiger / Quadtrac Tractors: 350 to 600 HP models
• Case IH Puma Tractors: 210, 220, 235, 250, 260, 270
• Case IH Farmall Tractors: 110A, 120A, 130A, 140A (Tier 4B)
• Case IH CX-Series Excavators: CX170E, CX220E, CX260E

1. 1

   Visually inspect the wiring harness running from the DCU to the Coolant Control Valve and the Reductant Purge Control Valve for chafing, melted insulation, or pinch points touching the frame

2. 2

   Disconnect the electrical connector at the Coolant Control Valve and the DCU, then use a multimeter to measure resistance between the UB3 supply pin and chassis ground (should be an open circuit)

3. 3

   Check the internal resistance of the Coolant Control Valve and the Reverting Valve to ensure an internal solenoid short is not pulling the UB3 circuit to ground

4. 4

   Ensure the DEF tank heating valve is not stuck open or leaking coolant

1. 1

   Preparation

   Turn off the ignition key, disconnect the battery to prevent further electrical damage, and allow the engine/coolant to cool down.

2. 2

   Harness Repair

   If the diagnostic checks revealed a short in the wiring harness, locate the damaged section. Splice and solder the broken wires, seal with heat-shrink tubing, and re-route the harness away from sharp edges or high-heat sources.

3. 3

   Valve Replacement

   If the valve is internally shorted: Drain the engine coolant to a level below the Coolant Control Valve to prevent spills. Disconnect the electrical connector from the Coolant Control Valve / Reductant Purge Valve. Loosen the hose clamps and remove the coolant lines from the valve. Remove the retaining bolts securing the valve support bracket (e.g., M14 bolts). Install the new Coolant Control Valve assembly. Torque the retaining bolts to OEM specifications (e.g., 99 - 108 N·m / 73 - 80 lb-ft for Farmall models). Reconnect the coolant hoses and the electrical connector.

4. 4

   Reassembly and Testing

   Refill the engine coolant and bleed the cooling system of air. Reconnect the battery.

5. 5

   Clear Codes

   Connect a diagnostic scan tool to the machine, clear the 19084 / P20A2 fault codes from the DCU, and run the engine to verify the code does not return.