Case IH 19079 (DTC 1A4A) - ECU – Engine Control Unit (ECU) or SCR/DEF Dosing Control Unit (DCU): DEF/AdBlue over pressure failure

The emissions system has detected that the fluid pressure in the Diesel Exhaust Fluid (DEF) supply line has exceeded the maximum operating threshold (typically around 9 bar / 130 psi), which usually triggers an engine power derate to protect the SCR system.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (e.g., 7240, 8240, 9240)
• Puma Series (130-240, 185)
• Maxxum Series (115-150)
• Farmall Series (110A-140A)
• Magnum Series

1. 1

   Inspect the dosing injector for mechanical clogging, crystallization, or a collapsed spray pattern

2. 2

   Check DEF delivery lines between the pump and the injector for kinks, blockages, or frozen fluid

3. 3

   Verify DEF fluid quality in the tank for contamination or crystallization

4. 4

   Inspect the wiring harness near the exhaust for cracked insulation, heat damage, or intermittent shorts

5. 5

   Scan the ECU history for related reverting valve failures (e.g., 19082, 19083) or temperature codes that point to a frozen system

1. 1

   Flush the System

   If the DEF fluid is degraded or contaminated, drain the tank and flush the system completely before installing new parts.

2. 2

   Clear Blockages

   If the dosing injector is clogged with crystallized DEF, attempt to clean it using warm distilled water. If the mechanical blockage cannot be cleared, replace the dosing injector.

3. 3

   Test the Pump

   If the lines and injector are completely clear but the over-pressure code persists, the internal pressure sensor or regulator within the DEF pump (supply module) has likely failed.

4. 4

   Replace the DEF Pump

   Remove the faulty DEF pump assembly (often tank-mounted or frame-mounted depending on the architecture) and install the replacement unit.

5. 5

   Program the Module

   A new Bosch Denoxtronic supply module must be programmed/calibrated to the vehicle's ECU after installation.

6. 6

   Clear Codes and Test

   Clear the fault codes using a diagnostic scan tool and run a forced regeneration or system test to verify the DEF pressure remains within the normal operating range.