Case IH 19806 – DCU (Dosing Control Unit): UREA (DEF) Tank Temperature Not Plausible / SRC Low

The UREA (DEF) tank temperature is 'not plausible' when compared to the temperature of the DEF pump module. The system has detected a SRC Low (Short Circuit Low) condition, meaning the raw voltage signal coming from the DEF tank temperature sensor is too low, which typically points to a short to ground in the sensor itself or within its wiring circuit. The SCR system cannot accurately dose the fluid or trigger the DEF tank heater.

• Tier 4a
• Tier 4B
• Steiger 350
• Steiger 400
• Steiger 450
• Steiger 500
• Steiger 550
• Steiger 600
• Magnum 235
• Magnum 315
• Magnum 340
• Puma
• Maxxum
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230

1. 1

   Visually inspect the DEF tank sending unit (DEF Head Unit) wiring harness for chafing, pinched wires, or melted insulation that could cause a short to ground.

2. 2

   Disconnect the electrical connector at the DEF tank sensor and check for water intrusion, DEF fluid crystallization, or bent pins that can bridge connections.

3. 3

   With the sensor disconnected, use a multimeter to check the signal wire leading back to the DCU for continuity to ground. Continuity indicates the wiring harness is shorted.

4. 4

   Measure the resistance across the temperature sensor pins on the DEF header unit. A reading near zero indicates a dead short and internal sensor failure.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical spikes.

2. 2

   Harness Repair

   If the diagnostic tests revealed a short to ground in the wiring harness, locate the damaged section, splice in new wiring using weather-sealed connectors, and wrap it in protective loom.

3. 3

   Sensor Replacement

   Clean the area around the top of the DEF tank thoroughly to prevent dirt from falling into the tank. Disconnect the electrical harness and the DEF suction/return lines from the top of the DEF header. Unscrew the locking ring or remove the mounting bolts securing the DEF head unit to the tank. Carefully extract the old DEF head unit assembly. Install the new DEF head unit, ensuring the rubber O-ring/gasket is properly seated to maintain a watertight seal. Reattach the DEF lines and plug in the electrical connector.

4. 4

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a diagnostic scan tool to clear the 19806 / P205C fault code. Run the engine and verify that the DCU is now reading a plausible DEF tank temperature.