Case IH F-4334-16 - ECU – Engine Control Unit (ECU): Supply module pressure during dosing above threshold / High DEF dosing pressure error

The system has detected that the Diesel Exhaust Fluid (DEF) supply pressure has exceeded the maximum allowable threshold value while the system is actively dosing.

• MAGNUM AFS Connect
• Magnum (180-370)
• Steiger (350-600)
• Puma (130-215)
• Maxxum (110-140)
• Farmall
• 240 Series
• 5130
• 6130
• 7130
• 7230
• 8230
• 9230
• Patriot (2250, 3240, 3340, 4430)
• Titan
• Farmlift series

1. 1

   Inspect all DEF suction and pressure lines for pinches, kinks, or physical blockages (addresses pinched/blocked DEF line).

2. 2

   If operating in freezing temperatures, ensure the DEF tank heater and line heaters are functioning, as frozen urea can trigger this code (addresses incomplete defrosting).

3. 3

   Inspect the DEF dosing valve (injector) at the exhaust for crystallization blockages or being stuck open/closed (addresses stuck or blocked dosing valve).

4. 4

   Check the wiring harness to the DEF pressure sensor and supply module for shorts to ground or open circuits (addresses sensor/wiring failure).

5. 5

   Verify the accuracy of the pressure sensor reading using a diagnostic scan tool (addresses sensor failure).

1. 1

   Preparation

   Turn off the ignition switch and wait for the ECU to power down completely and for communication with the diagnostic scan tool to discontinue. Ensure the DEF system has depressurized and purged fluid back to the tank.

2. 2

   Disconnect Hoses

   Locate the DEF supply module. Disconnect the DEF supply and return hoses. Note: Squeeze the locking tabs together and pull straight upward on the elbow connectors to release them without breaking the plastic fittings.

3. 3

   Disconnect Electrical

   Unplug the main wiring harness connector(s) from the DEF supply module.

4. 4

   Removal

   Remove the mounting bolts/hardware securing the module to its bracket or the DEF tank flange, and remove the pump assembly.

5. 5

   Installation

   Mount the new DEF supply module and secure the hardware. Reconnect the electrical harness and snap the DEF hoses back into place, ensuring the locking tabs click securely.

6. 6

   Programming & Calibration

   CRITICAL STEP. A new DEF supply module must be programmed/calibrated to the vehicle's ECU after replacement.

7. 7

   Clear Codes

   Use the diagnostic scan tool to clear the F-4334-16 fault code (and any related codes like P20C9). Turn the ignition on without starting the engine to verify codes do not immediately return, then run the machine to verify proper dosing pressure.