Case IH 19804 – DCU: DEF Tank Temperature Sensor Open Circuit

The Dosing Control Unit (DCU) detects an open circuit in the DEF tank temperature sensor circuit. This missing or erroneous signal causes a temperature discrepancy between the DEF tank and the DEF pump module, preventing the Selective Catalytic Reduction (SCR) system from accurately monitoring DEF conditions to prevent freezing and ensure proper dosing.

• Tier 4a
• Steiger (350, 400, 450, 500, 550, 600 NA/QT)
• Puma (130 through 240)
• Magnum (MX210 through MX285)
• Maxxum (115 through 150)
• Optum (270, 300)
• Farmall (90C, 110U)
• Axial-Flow (7230, 8230, 9230)
• Windrowers (WD1204 through WD2504)

1. 1

   Visually inspect the wiring harness between the DEF tank temperature sensor and the DCU for broken wires, chafing, or disconnected plugs.

2. 2

   Disconnect the sensor harness and check for corroded, bent, or pushed-out pins.

3. 3

   Use an Electronic Service Tool (EST) or compatible scan tool to verify if DTC P205A is currently active or stored in history.

4. 4

   Ensure the DEF fluid is not contaminated, as poor-quality fluid can damage the sending unit.

1. 1

   Repair wiring harness

   If a broken wire or damaged connector is found during inspection, repair the open circuit in the harness and reconnect the sensor.

2. 2

   Replace DEF sensor unit

   If the wiring is intact and receiving proper voltage, the internal temperature sensor has failed. Replace the entire DEF Head Unit assembly (or standalone sensor depending on model).

3. 3

   Clear fault codes

   After replacing the unit or repairing the wire, reconnect the battery/power, turn the ignition on, and use a diagnostic scan tool to clear the DCU/ACM fault codes.

4. 4

   Test operation

   Run the machine to ensure the DCU is reading plausible DEF tank temperatures and that the Malfunction Indicator Lamp (MIL) remains off.