Case IH 3971 – Engine Control Unit (ECU): After run relay high side driver circuit short to ground failure

The control module has detected a short to ground on the high-side control circuit that activates the 'After Run' relay. This relay keeps the DEF/AdBlue supply module powered for a brief period after engine shutoff to purge the DEF fluid out of the lines and back into the tank, preventing freezing and cracking.

• Steiger T4B
• 240 Series Axial-Flow Combines
• Magnum Series
• Maxxum Series
• Steiger Series
• Farmall Series

1. 1

   Check the Electronic Service Tool (EST) for related codes (such as 3764 / DTC F561 - ECU after-run power interrupted) and diagnose them first

2. 2

   Locate the After Run Relay (often designated as K-063) and test for an internal short circuit using a multimeter

3. 3

   Disconnect the harness at the ECU and at the relay block, then check the high-side driver wire for continuity to ground to identify chafing or insulation damage

4. 4

   Inspect the fuses associated with the engine auxiliary relays and ignition switch circuits for blown fuses caused by the short

1. 1

   Disconnect Power

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

2. 2

   Replace Faulty Relay

   If the After Run Relay failed the internal short test, discard it and install a new OEM relay.

3. 3

   Repair the Wiring Harness

   If the relay is good but the circuit is shorted, trace the wire from the ECU to the relay block. Locate the chafe mark or pinch point. Cut out the damaged section of wire, solder in a new section, and seal it with heat-shrink tubing.

4. 4

   Replace Blown Fuses

   Check and replace any blown 5A or 25A fuses on the relay control or load circuits.

5. 5

   Reassemble and Clear Codes

   Reconnect the battery. Connect the Case IH Electronic Service Tool (EST) and clear the inactive fault codes.

6. 6

   Verification Test

   Start the engine, let it run for a minute, and then shut it down. Listen for the DEF pump running its purge cycle. Verify that the code does not return after the purge cycle completes.