Case IH 19758 – Engine Control Module (ECM) or Aftertreatment Control Module (ACM) / Doser Electronic Control Unit (DCU): Ratio between DEF/AdBlue Pump Speed and Dosing Valve exceeded

This code indicates a mismatch between the commanded state of the DEF (Diesel Exhaust Fluid) dosing valve and the operational speed of the DEF supply pump. The DEF pump is running at a disproportionately high speed compared to the amount of fluid the dosing valve is commanded to inject. This typically points to an inability to build or maintain proper DEF system pressure (usually around 100-140 PSI / 9 bar).

• Tier 4b
• Case IH Steiger
• Case IH Magnum
• Case IH Puma
• Case IH Optum

1. 1

   Visual Leak Inspection: Clean the DEF pump, dosing valve, and all supply lines. Run a system pressurization test using the CNH Electronic Service Tool (EST) and inspect for external fluid leaks or crystallized DEF buildup.

2. 2

   Electrical Testing: Inspect the wiring harness and connectors to the dosing valve and pump for corrosion or damage. Test the resistance of the dosing valve using a multimeter; a healthy doser injector valve should read between 11 to 18 ohms.

3. 3

   Filter Check: Ensure the main DEF pump filter is not plugged, which can cause the system to pull a vacuum and force the pump to over-speed.

4. 4

   Dosing Quantity & Pressure Test: Using the diagnostic software, run a DEF pump priming test followed by a DEF doser test. Place a measuring cup under the removed doser valve. The system should build to standard pressure (approx. 100-140 PSI) and dispense the correct volume of fluid (typically 3.5 to 4.5 oz depending on the specific engine spec). If the pump fails to build pressure but has power and no leaks, the pump has failed internally.

1. 1

   If replacing the DEF Dosing Valve: Turn off the machine and wait for the DEF system to complete its automatic purge cycle (listen for the pump reverting fluid back to the tank). Disconnect the battery.

2. 2

   Disconnect the electrical harness and the DEF supply line from the dosing valve located on the SCR decomposition tube.

3. 3

   Remove the mounting clamp or bolts securing the valve.

4. 4

   Clean the mounting surface on the exhaust tube thoroughly to ensure a proper seal.

5. 5

   Install the new dosing valve with a new OEM gasket/seal. Torque the clamp/bolts to manufacturer specifications.

6. 6

   Reconnect the DEF line and electrical harness.

7. 7

   If replacing the DEF Supply Pump: Ensure the system is purged and the battery is disconnected.

8. 8

   Disconnect the electrical connectors, the DEF fluid lines, and the coolant lines (if equipped) from the pump module.

9. 9

   Unbolt the pump assembly from its mounting bracket and remove it from the machine.

10. 10

    Mount the new DEF pump and secure the bolts.

11. 11

    Reconnect all fluid lines, coolant lines, and electrical connectors.

12. 12

    Post-Repair: Reconnect the battery. Use the CNH diagnostic tool to prime the system, check for leaks, clear the 19758 fault code, and perform a parked SCR system test to verify the repair.

    A new pump module may require programming/calibration to the vehicle's ACM.