Case IH 19083 – DCU (Dosing Control Unit): Voltage supply 3 - Coolant control valve and reverting valve (UB3) electrical | Open circuit to UB3 | P20A0 Vent valve (Reductant Purge Control Valve) - open circuit.

The system has detected an open electrical circuit on the UB3 voltage supply line. This circuit provides power to the DEF (Diesel Exhaust Fluid) coolant control valve and the reverting valve (also known as the reductant purge control valve). When this circuit is open, the system cannot properly control the flow of engine coolant used to thaw/heat the DEF tank, nor can it purge the DEF lines when the machine is shut down.

• Tier 4a
• Magnum series (180-370, including Series 4)
• Steiger series (350-600)
• Puma series
• Maxxum series
• Axial-Flow 5130
• Axial-Flow 6130
• Axial-Flow 7130
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230
• Patriot 4430
• Titan series
• Farmlift series
• CX series excavators

1. 1

   Turn off the ignition and visually inspect the wiring harness between the DCU and the coolant control valve/reverting valve.

2. 2

   Verify that all electrical connectors at the DEF supply module are securely seated and free of corrosion, bent pins, or moisture.

3. 3

   Use a multimeter to check for an open circuit or broken wire on the UB3 voltage supply line.

4. 4

   Check the internal resistance of the coolant control valve solenoid to ensure the coil itself has not failed open.

1. 1

   Secure Connections

   Disconnect and reconnect the main harnesses at the DEF Supply Module and the Coolant Control Valve to ensure a tight electrical contact.

2. 2

   Repair Wiring

   If your multimeter continuity test reveals a break in the UB3 circuit between the DCU and the valve, repair the damaged section of the wiring harness.

3. 3

   Clear and Retest

   Clear the 19083 / P20A0 fault code using a diagnostic scan tool. Turn the ignition on without starting the engine and observe if the code returns.

4. 4

   Replace the Module

   If the wiring is completely intact, the connectors are secure, and the fault code immediately reoccurs or cannot be cleared, the DCU has suffered an internal hardware failure on the UB3 driver circuit. You must replace the DEF Supply Module (NOx neutralization unit).

5. 5

   Post-Repair

   After replacing the module, clear all DCU DTCs and run a system test to ensure the reductant purge control valve operates normally.