Case IH 19352 – DCU (Dosing Control Unit): Reverting valve (4-2way valve?) mechanically | valve does not open | P20A0 Vent valve (Reductant Purge Control Valve) - open circuit

Failure within the Diesel Exhaust Fluid (DEF) / Urea dosing system where the reverting valve (reductant purge control valve or vent valve) is either mechanically stuck in the closed position or has an electrical open circuit, preventing it from relieving pressure and purging DEF back into the tank when the system shuts down.

• Tier 4a
• Tier 4b
• Magnum 180–370
• STX Steiger 350–600
• Puma 130–215
• Maxxum 110–140
• 5130–9230 Combines
• Patriot/Titan Sprayers
• T8.xxx Series
• T7 Series (T7.170–T7.260)
• T6 Series

1. 1

   Clear the DTC with a diagnostic scan tool. Turn the ignition off, wait for communication to drop, then turn the ignition back on without starting the engine to see if the code immediately resets.

2. 2

   Inspect the control circuit wiring between the DCU and the DEF Supply Module. Look for open circuits, chafed wires, or loose/corroded pins at the connector.

3. 3

   Perform a pressure drop test: if the DEF pressure exceeds 450 kPa at normal operating speed and the cooling valve is open, the pressure must drop by at least 15 kPa within 2 seconds when commanded. If it does not, the reverting valve is mechanically jammed.

4. 4

   Visually inspect the external housing of the DEF pump for dried white urea crust, which indicates a leak or freezing damage that may have seized the internal mechanicals.

1. 1

   Turn OFF the ignition switch and disconnect the battery to ensure the DCU is powered down.

2. 2

   Drain the DEF fluid from the supply module lines.

3. 3

   Disconnect the electrical harness and the DEF fluid lines (suction, pressure, and backflow) from the DEF Supply Module.

4. 4

   Unbolt and remove the faulty DEF Supply Module from its mounting bracket.

5. 5

   Install the replacement DEF Supply Module.

   Ensure the surrounding area is completely clean of dried urea crust and dust before opening any caps to safeguard the internal high-pressure fluid loops.

6. 6

   Reconnect the fluid lines and electrical harness.

7. 7

   Reconnect the battery, turn the ignition ON, and use a scan tool to clear the DCU DTCs (including P20A0 and any related codes like P20C9).

8. 8

   Run a system test or start the engine to allow the pump to build pressure and verify that the reverting valve operates correctly upon shutdown without throwing the code.