Case IH 19651 – DCU / ECU: DEF/AdBlue tank level sensor voltage too low.

The control module is receiving a voltage signal from the Diesel Exhaust Fluid (DEF) tank level sensor that is below the normal operating range (Short Circuit Low). This fault typically triggers an SCR inducement (engine derate or speed limitation) to prevent the machine from running without emissions control.

• Tier 4b
• Magnum 235-340 (Series 4)
• Steiger series (350-600 HP)
• Farmall 90C
• Farmall 110U
• 240 Series Combines (7240, 8240, 9240)
• W190C Wheel Loader
• W230C Wheel Loader
• TR340 Compact Track Loader
• STM N Series Loaders

1. 1

   Inspect the wiring harness between the DEF tank level sensor and the DCU/ECU for chafing, melting, or a short circuit to ground.

2. 2

   Disconnect the DEF header unit connector and inspect the pins for corrosion, moisture intrusion, or pushed-out pins.

3. 3

   Verify CAN Bus communication and check for related network codes (e.g., 19652 or 19653) to rule out a network issue.

4. 4

   Check the DEF tank fluid for crystallization or contamination that could physically damage the sensor float or probes.

1. 1

   Prep the Machine

   Turn off the machine and disconnect the battery. Clean the area around the top of the DEF tank to prevent dirt from falling into the tank.

2. 2

   Drain the Tank

   Drain the DEF fluid from the tank. If the fluid is contaminated, the tank must be thoroughly flushed before installing the new sensor to prevent immediate damage to the new unit.

3. 3

   Disconnect the Header

   Unplug the electrical connector and disconnect the DEF suction and return lines from the top of the DEF header unit.

4. 4

   Remove the Sensor Assembly

   Remove the mounting flange/seal securing the DEF head unit to the tank. Carefully pull the long sensor assembly straight up and out of the tank.

5. 5

   Install the New Part

   Insert the new DEF head unit into the tank, ensuring the new rubber seal is seated correctly to prevent leaks. Secure the mounting flange.

6. 6

   Reconnect

   Reconnect the DEF lines and the electrical connector.

7. 7

   Refill and Clear Codes

   Refill the tank with fresh, high-quality DEF. Reconnect the battery, use a diagnostic tool to clear the 19651 fault code, and run an engine cycle to ensure the SCR inducement/derate is lifted.