Case IH 19875 – Heater Control Unit (HCU): PRC high for voltage at DEF/AdBlue Supply module Heater (via HCU)

The system has detected a voltage level that is higher than the expected range on the circuit responsible for heating the Diesel Exhaust Fluid (DEF) supply module (pump). This condition typically points to a short to voltage in the wiring harness, a failed internal heater element within the DEF supply module, or an internal failure of the Heater Control Unit itself.

• Tier 4b
• Magnum (180-370)
• Maxxum (110-140)
• Puma (130-215)
• Steiger (350-600)
• Vestrum
• Farmall (95A, 100C, 110C)
• Axial-Flow series (5130-9230)
• Patriot
• Titan sprayers
• N Series Backhoe Loaders (e.g., 580SN)
• Farmlift Telehandlers

1. 1

   Inspect the wiring harness running from the HCU to the DEF Supply Module for chafing, melted insulation, or pinched wires that could cause a short to battery voltage.

2. 2

   Disconnect the harness at the DEF Supply Module and the HCU. Check for corrosion, moisture (DEF fluid intrusion/crystallization), or bent pins.

3. 3

   Measure the resistance of the DEF Supply Module Heater element pins to ensure it is within OEM specification and not internally shorted.

4. 4

   Verify that the HCU is receiving proper voltage at Terminal 30 and has a clean ground connection.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery to prevent electrical spikes during the repair.

2. 2

   Access the DEF Supply Module

   Locate the DEF supply module (pump), which is typically mounted directly to or near the DEF tank.

3. 3

   Repair Wiring (If Applicable)

   If the diagnostic checks revealed a short to voltage in the harness, repair the damaged section of the wiring or replace the harness segment.

4. 4

   Replace the DEF Supply Module (If Heater is Failed)

   Because the heater element is integrated into the DEF supply module on these Bosch Denoxtronic systems, a shorted heater requires replacing the entire supply module assembly. Disconnect the DEF fluid lines (suction, pressure, and backflow). Remove the mounting bolts and extract the old module. Install the new module, ensuring the surrounding area is completely clean of dried white urea crust to prevent contamination.

5. 5

   Replace the HCU (If Module/Wiring Test Good)

   If the wiring is intact and the supply module heater tests within spec, the HCU has failed internally and must be replaced.

6. 6

   Reassembly and Testing

   Reconnect the battery. Connect the Case IH EST to clear the 19875 fault code. Run a DEF system prime and dosing test via the EST to verify the heater circuit is operating within the correct voltage parameters.