Case IH 19077 (DTC 334A) - ECU – Engine Control Unit (ECU): DEF/AdBlue pressure stabilization failure

The Selective Catalytic Reduction (SCR) system is unable to build, stabilize, or maintain the required pressure of Diesel Exhaust Fluid (DEF) in the lines between the DEF supply module (pump) and the dosing injector, triggering an emissions-related engine derate.

• MAXXUM T4E
• 240 Series Axial-Flow (7240, 8240, 9240)
• 130/230 Series (5130, 6130, 7130, 7230, 8230)
• Magnum (180 through 380)
• Steiger/Quadtrac (350 through 620)
• Puma (130 through 240)
• Maxxum series
• Patriot (4430)
• Titan series
• Farmlift series
• Case/Kobelco excavators

1. 1

   Verify the DEF tank has adequate fluid and that the fluid is not degraded, contaminated, or frozen.

2. 2

   Look for heavy white urea crystallization around the pump, lines, and injector, which indicates a leak.

3. 3

   Check the DEF supply and return lines for pinhole leaks, kinks, or blockages.

4. 4

   Check for a restricted DEF supply module filter clogged by micro-contaminants or crystallized urea sediment (the most common cause).

5. 5

   Using the Case IH Electronic Service Tool (EST) or equivalent PT-Box, command a Urea Dosing System Test (UDST) to monitor actual pressure versus commanded pressure.

6. 6

   Check for accompanying cascading codes such as DTC 4B8A or DTC 335A, which point directly to a failed pump motor.

1. 1

   Clean the Area

   Thoroughly clean the exterior of the DEF supply module. Ensure the surrounding area is completely free of dried white urea crust and dust before opening the filter cap. If flushing the external housing face, use only clean distilled water to safeguard the internal high-pressure fluid loops.

2. 2

   Replace the Main DEF Filter

   Open the filter cap on the supply module. Use the specialized extraction tool to carefully pull out the old filter element (Caution: Do not scratch the inner walls of the pump housing reservoir). Install the new high-efficiency media block filter and replace the cap/seals.

3. 3

   Replace the DEF Supply Module

   If the pump still cannot stabilize pressure after a filter change, the internal pump diaphragm or motor has failed. Disconnect the electrical harness, supply line, and return line, then unbolt and replace the entire DEF Supply Module assembly.

4. 4

   System Prime and Test

   Use the diagnostic tool to perform 3 consecutive Urea Dosing System Tests (UDST) following the on-screen instructions to bleed air from the lines and verify stable pressure.

5. 5

   Reset ECU Inducement

   Perform the 'Inducement Unlock / Counter Reset' via the diagnostic tool to restore full engine power.