Case IH 19653 – DCU (Dosing Control Unit): UREA Tank level error (CAN message or electrical with real sensor) – Level over CAN: SAE J1939 Erroneous Signal / Level sensor connected directly: SRC low (too many CAN messages)

The controller is receiving an erratic, out-of-range, or excessive number of CAN bus messages from the Diesel Exhaust Fluid (DEF / Urea) tank level sensor. The "SRC low" designation indicates a "Short Circuit Low," meaning there is likely a short to ground in the sensor's electrical circuit or an internal failure within the sensor itself causing communication to crash or spam the CAN network.

• Tier 4a
• Tier 4b
• Case IH Magnum (e.g., 235–340 Series 4)
• Case IH Steiger (e.g., 350–600)
• Case IH Puma
• Case IH Maxxum
• Case IH Farmall (Tier 4B models)

1. 1

   Inspect the wiring harness between the DEF tank level sensor (located on top of the DEF tank) and the DCU. Look for chafed wires causing a short to ground (SRC low).

2. 2

   Disconnect the DEF level sensor. Check the connector pins for corrosion, moisture intrusion (crystallized DEF fluid), or pushed-out pins, which commonly cause erratic CAN signals.

3. 3

   Using a multimeter, verify the SAE J1939 CAN bus lines for proper resistance (typically 60 ohms across the network) and ensure there is no short between CAN High and CAN Low.

4. 4

   Look for other DCU codes (like 19676 or 19102) which might indicate a broader CAN communication failure or a shared ground issue.

1. 1

   Prep the Machine

   Turn off the ignition and disconnect the battery to prevent electrical spikes.

2. 2

   Access the DEF Tank

   Locate the DEF tank and thoroughly clean the area around the top of the tank to prevent dirt from falling in.

3. 3

   Drain Fluid (If necessary)

   Drain the DEF fluid below the level of the header, or completely if you plan to clean the tank.

4. 4

   Remove the DEF Header

   Disconnect the electrical connector and the DEF fluid lines from the header unit. Remove the mounting bolts or retaining ring securing the header to the tank.

5. 5

   Extract and Replace

   Carefully pull the old DEF header/level sensor assembly out of the tank. Install the new unit, ensuring the rubber O-ring/gasket is properly seated to prevent leaks.

6. 6

   Reassemble

   Reconnect the DEF lines and the electrical connector. Refill the tank with fresh, uncontaminated Diesel Exhaust Fluid.

7. 7

   Clear Codes

   Reconnect the battery. Turn the key to the ON position and use a diagnostic scan tool (or the tractor's onboard diagnostic menu) to clear the stored 19653 and P203C fault codes.

8. 8

   Verify

   Start the engine and verify that the DEF level gauge on the dash reads correctly and the fault code does not return.