Case IH 19651 – DCU (Dosing Control Unit): UREA (DEF) Tank Level Error / Ambient Temperature Error

Fault code 19651 indicates the DEF tank level sensor is sending an erroneous signal over the SAE J1939 CAN bus, or has a short circuit to a low voltage source. Fault code 19676 indicates the control module is checking the CAN bus for the ambient air temperature signal, but it is out of range, erroneous, or unavailable due to a serial communication link failure.

• Tier 4a
• Case IH Magnum 235 - 340 (Series 4)
• Case IH Steiger Series (350 to 600 HP)
• Case IH Farmall 90C
• Case IH Farmall 100C
• Case IH Maxxum 150

1. 1

   If diagnosing 19651: Check the DEF fluid level manually to ensure the tank is not completely empty or overfilled.

2. 2

   If diagnosing 19651: Inspect the DEF tank level sensor wiring harness for a short to ground (which triggers the SRC low condition).

3. 3

   If diagnosing 19651: Check the CAN bus communication lines at the DEF tank header for corrosion or backed-out pins.

4. 4

   If diagnosing 19676: Verify the physical condition of the Ambient Air Temperature Sensor (often integrated with the humidity sensor on the intake).

5. 5

   If diagnosing 19676: Check the SAE J1939 CAN bus wiring between the ambient temp sensor, the Engine ECU, and the DCU for open circuits or high resistance.

1. 1

   Save and Clear the Error Log

   First, save the error log in your diagnostic tool, then erase it. Restart the ECU/machine to see if the fault returns as an active code.

2. 2

   Inspect the Harness

   Locate the affected sensor (DEF header unit for 19651; Ambient Air Temp sensor for 19676). Disconnect the pigtail and inspect the connector for water intrusion, bent pins, or corrosion.

3. 3

   Test the Circuit

   Use a multimeter to check for continuity and verify that the sensor is receiving the correct reference voltage from the DCU. For code 19651, specifically test for a short to ground on the signal wire.

4. 4

   Replace the Sensor

   If the wiring is intact and communication lines are healthy, the sensor itself has failed internally. Replace the DEF tank level sending unit or the Ambient Air Temperature sensor.

5. 5

   Re-calibrate and Clear

   After installing the new part, turn the key to the ON position, clear the inactive codes, and run the engine to verify that the CAN bus is successfully receiving the sensor signals and that emission derates are lifted.