Case IH 19094 – DCU (Dosing Control Unit): Monitoring VDD11/ VDD25 voltage - Dosing valve/pump motor supply voltage VD25 low - P0658 12 Volt supply for dosing module - Below lower limit

The 12-volt electrical supply to the DEF (Diesel Exhaust Fluid) dosing module—specifically the circuit powering the dosing valve or pump motor actuator—has dropped below the acceptable lower voltage limit.

• Tier 4a
• Steiger
• Magnum (180-380)
• Puma (140-240)
• Maxxum (115-150)
• Optum
• Farmall
• Axial-Flow 5130
• Axial-Flow 6130
• Axial-Flow 7130
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230
• Axial-Flow 40/50/60 series
• Patriot
• Farmlift

1. 1

   Verify the main battery voltage and check the voltage supply directly at the DCU.

2. 2

   Inspect the wiring harness between the DCU, the DEF dosing pump module, and the DEF dosing valve for chafed wires, shorts to ground, or corroded pins.

3. 3

   Ensure the DEF system is not frozen (common in cold weather); the system must be fully thawed before accurate diagnosis.

4. 4

   Perform an actuator test on the dosing valve using a diagnostic tool to check UREA pressure drop and monitor for voltage dropouts.

1. 1

   Test Power Supply

   Check the fuses and relays that supply power to the DCU and the DEF system. Replace any blown fuses and test relays for proper operation.

2. 2

   Harness Repair

   Disconnect the electrical connectors at the DEF dosing pump and the dosing injector valve. Use a multimeter to verify that a full 12 volts is reaching the components when the key is ON. If voltage is low, trace the harness back to the DCU and repair any damaged wiring.

3. 3

   Component Replacement

   If the wiring is intact and the DCU is outputting the correct voltage, but the fault persists, the internal circuitry of the DEF Dosing Pump Module or the Dosing Valve is likely shorted or failing. Replace the faulty component.

4. 4

   Programming

   If the DEF Dosing Pump Module is replaced, the new module will need to be programmed/calibrated to the vehicle using the Case IH EST diagnostic software.

5. 5

   Clear and Verify

   Clear the fault codes from the DCU. Run the machine to allow the DEF system to build pressure and begin dosing to verify the repair is successful.