Case IH 19757 – DCU (Dosing Control Unit): Reagent Pump Not Delivering / Compressed Air Regulation Valve

19757 (P208B): The system has detected that the DEF (Diesel Exhaust Fluid / Urea) supply module/pump is failing to build pressure or deliver fluid to the dosing injector. 19766 (P20A7): The system has detected an electrical or mechanical fault in the compressed air regulation valve, which is responsible for managing the air pressure used to atomize the DEF fluid.

• Tier 4a
• Case IH Magnum: 235, 260, 290, 315, 340 (Series 4)
• Case IH Steiger & Quadtrac: 350, 400, 450, 500, 550, 600
• Case IH Rowtrac: 350, 400, 450, 500

1. 1

   For 19757 (P208B - Reagent Pump): Verify the DEF tank is not empty and that the fluid is not degraded or crystallized.

2. 2

   For 19757 (P208B - Reagent Pump): Check the DEF suction and pressure lines for kinks, blockages, or severe leaks.

3. 3

   For 19757 (P208B - Reagent Pump): Inspect the wiring harness connecting the DCU to the DEF pump. Look for damaged wires, loose connector pins, or corrosion (especially from pressure washing).

4. 4

   For 19757 (P208B - Reagent Pump): Check the DEF pump main filter for severe clogging or crystallization.

5. 5

   For 19766 (P20A7 - Air Regulation Valve): Verify that the tractor's pneumatic system is generating and holding adequate air pressure.

6. 6

   For 19766 (P20A7 - Air Regulation Valve): Check the electrical connector at the air regulation valve for a short to ground, short to battery, or open circuit. Ensure the pins are tight and free of moisture.

7. 7

   For 19766 (P20A7 - Air Regulation Valve): Listen and inspect for compressed air leaks between the air supply tank, the regulation valve, and the dosing nozzle.

1. 1

   Clear and Retest

   Connect the CNH Electronic Service Tool (EST). Clear the inactive codes and run the engine to operating temperature to see if the fault returns as active.

2. 2

   Harness Repair

   If continuity tests reveal a short or open circuit in the wiring to either the pump or the valve, repair the damaged section of the harness or replace the connector pigtail.

3. 3

   Component Replacement

   If diagnosing 19757 and the wiring/lines are good, replace the DEF Reagent Pump (Supply Module) and its internal filter. If diagnosing 19766 and the wiring/air supply are good, replace the Compressed Air Regulation Valve.

4. 4

   System Bleed and Test

   After replacing SCR components, use the EST to run a "System Leakage Test" and a "Dosing Test" to prime the system, verify that the pump builds pressure, and ensure the air valve atomizes the fluid correctly.

5. 5

   Final Validation

   Clear all DCU/ECU fault codes and operate the machine under load to ensure the SCR system is functioning and no codes return.