Case IH 3882 (DTC 777D) - ECU – DCU (Dosing Control Unit): Supply UB2 short circuit to ground failure

This code indicates that the control module has detected a short to ground on the 'UB2' voltage supply circuit, which supplies voltage to the DEF suction tube heaters. When this circuit shorts to ground, the DEF heating system cannot function, which will eventually lead to an emissions derate.

• MAXXUM T4E
• 240 Series Combines (7240, 8240, 9240)
• Steiger
• Magnum
• Puma
• Maxxum
• Patriot Series Sprayers (3240, 3340)

1. 1

   Visually inspect the wiring harness leading to the DEF Pump/Dosing Control Unit for chafed, melted, or pinched wires that could be grounding out against the machine's frame.

2. 2

   Perform a harness isolation test by disconnecting the main electrical connector at the DEF pump module and using a multimeter to check for continuity to ground on the UB2 supply pins on the machine-side harness.

3. 3

   If the machine-side harness tests good (no short to ground), conclude that the short is internal to the DEF pump module.

1. 1

   Preparation

   Turn off the machine and turn off the battery disconnect switch. Ensure the DEF system has completed its purge cycle (wait at least 2 minutes after key-off before disconnecting batteries).

2. 2

   Disconnect

   Thoroughly clean the area around the DEF pump to prevent dirt from entering the SCR system. Disconnect the electrical harness connectors from the DCU.

3. 3

   Line Removal

   Disconnect the DEF suction, backflow, and pressure lines. Cap the lines immediately to prevent crystallization and contamination.

4. 4

   Removal

   Unbolt the DEF pump module from its mounting bracket (usually located near or on top of the DEF tank) and remove the unit.

5. 5

   Installation

   Mount the new DEF pump module and torque the bolts to OEM spec. Reconnect the DEF lines (listen for the 'click' on quick-connect fittings) and plug in the electrical connectors.

6. 6

   Programming

   A new Dosing Control Unit requires software installation and programming to the vehicle using the Case IH EST (Electronic Service Tool) laptop. CNH requires troubleshooting verification before issuing the passwords to flash the new module.