New Holland 19805 – DCU: Urea Tank Temperature Open Circuit

The system has detected a break or infinitely high resistance in the electrical circuit of the Diesel Exhaust Fluid (DEF) tank temperature sensor. This open circuit prevents the Dosing Control Unit (DCU) from monitoring the urea tank temperature, which is critical for the Selective Catalytic Reduction (SCR) system to reduce NOx emissions. Failure to monitor this temperature can lead to reduced engine performance, increased emissions, or the engine entering a derated limp mode.

• T6 Series
• T7 Series
• T8 Series
• T9 Series
• CR Series
• CX Series
• Patriot Series
• Farmall 110A
• Farmall 120A
• Farmall 130A
• Farmall 140A

1. 1

   Reboot the system by turning the machine off and on again to ensure the error is not a temporary glitch

2. 2

   Visually inspect the wiring harness and electrical connector at the DEF tank sensor for frayed or broken wires, corrosion, moisture, or bent/loose pins

3. 3

   Use a diagnostic scan tool to check for other active or stored fault codes related to the SCR system

4. 4

   Check the DEF level and condition to ensure it is adequately filled, not frozen, clear, and has a concentration of 32.5% (using a refractometer)

5. 5

   Test the circuit by disconnecting the harness from the sensor and checking for an open circuit or high resistance in the ground and signal wires between the DCU and the sensor connector

6. 6

   Check for voltage at the connector with the ignition on (expected voltage is 4.6 - 5.2 V)

7. 7

   Measure the resistance across the temperature sensor pins on the sender unit itself and compare to specifications (0°C/32°F - 942 ohms, 10°C/50°F - 608 ohms, 25°C/77°F - 330 ohms, 40°C/104°F - 189 ohms, 50°C/122°F - 133 ohms). An infinite or significantly out of range reading points to a failed sensor

1. 1

   Disconnect power

   Disconnect the vehicle's battery before starting any electrical repairs for safety.

2. 2

   Repair wiring

   If diagnostic checks reveal a break or corrosion in the wiring or connector, repair or replace the affected section of the harness. Ensure all connections are clean and secure.

3. 3

   Replace the DEF tank sender unit

   If the wiring is intact and the sensor is determined to be faulty, replace the entire DEF tank sender unit. Gain access to the top of the DEF tank, disconnect the electrical connector and fluid lines, unscrew the retaining ring or bolts, and carefully lift it out. Install the new sender unit, ensuring the seal is correctly seated, and tighten to manufacturer specifications.

4. 4

   Clear fault codes

   After the repair is complete, reconnect the battery and use a diagnostic tool to clear the 19805 fault code and any other related codes.

5. 5

   Verify repair

   Start the machine and let it run for several minutes to allow the system to self-test. Check to ensure the fault code does not reappear.