Case IH 19870 (F-4354-04) - ECU – Heater Control Unit (HCU): Short Circuit to Ground of DEF/AdBlue Pressure Line Heater Actuator powerstage

The control module has detected a short circuit to ground on the power circuit supplying the DEF pressure line heater. The DEF system uses heated lines to prevent the fluid from freezing in cold climates.

• VESTRUM CVX
• Case IH Puma
• Case IH Optum
• Case IH Magnum
• Case IH Steiger
• Case IH 240 Series Combines

1. 1

   Visually inspect the wiring harness running from the HCU/DEF Supply Module to the DEF pressure line heater for chafed, rubbed, or pinched wires that could be grounding out against the machine's chassis.

2. 2

   Inspect the electrical connector at the pressure line heater for corrosion, moisture ingress, or bent pins.

3. 3

   Isolate the short by disconnecting the DEF pressure line heater connector, turning the key on, and re-checking active fault codes. If the code changes to an open circuit (19871 or 4346 FMI 5), the short is internal to the heater element. If 19870 remains, the short is in the harness or HCU/DEF module.

1. 1

   Power Down

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

2. 2

   Access the DEF Lines

   Locate the DEF pressure line, which routes fluid from the DEF supply pump module to the dosing injector on the exhaust.

3. 3

   Harness Repair (If applicable)

   If the diagnostic check proved the harness was at fault, locate the damaged section of the wire, repair it using weather-sealed splice connectors, and secure the harness away from vibration points.

4. 4

   Line Replacement (If applicable)

   If the heater element inside the line is shorted: Disconnect the SAE J2044 quick-connect fittings at both ends of the DEF pressure line. Have a catch pan ready for spilled DEF. Unplug the electrical connector for the line heater. Remove the line from its retaining clips and route the new heated DEF line in the exact same orientation. Snap the quick-connect fittings into place and plug in the electrical connector.

5. 5

   Clear and Test

   Reconnect the battery, clear the inactive fault codes using a diagnostic scan tool, and run a DEF system leak/heater test to verify the repair.