Case IH 3968 – Engine ECU: After run relay high side driver circuit open failure

The control module has detected an open circuit (a break in the electrical connection, a blown fuse, or an unplugged component) on the high side (power supply side) of the after-run relay circuit. The after-run relay is responsible for keeping the engine control system powered for a brief period after the key is turned off, which is critical for the SCR (Selective Catalytic Reduction) system to purge DEF/AdBlue lines and save engine data.

• Steiger T4B
• Case IH 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Case IH Steiger Tractors
• Case IH Magnum Tractors
• Case IH Farmall Series

1. 1

   Check the 5 Amp mini fuse assigned to the after-run relay in the power distribution box for a blown condition.

2. 2

   Test the after-run relay for internal continuity to ensure the relay coil is not open.

3. 3

   Inspect the wiring harness between the Engine ECU and the after-run relay socket for chafed wires, disconnected plugs, or pushed-out pins.

4. 4

   Verify that battery voltage is present at the high side of the relay receptacle when the system is active.

1. 1

   Power Down

   Turn off the machine and disconnect the battery ground to ensure safety while working on the electrical system.

2. 2

   Inspect and Replace Fuse

   Locate the 5A after-run relay fuse. If it is blown, replace it with a new 5A beige mini-fuse.

3. 3

   Inspect and Replace Relay

   If the fuse is intact, test the after-run relay. If it fails a bench test (or if you are swapping it with a known good relay of the same type to test), replace the relay.

4. 4

   Harness Repair

   If both the fuse and relay are good, trace the wire from the relay block back to the Engine ECU. Repair any broken wires or clean any corroded connector pins.

5. 5

   Reassemble and Clear Codes

   Reconnect the battery, turn the key on, and use a diagnostic tool (like the Case IH EST) to clear the inactive fault codes.

6. 6

   Verify Repair

   Start the engine, let it run briefly, and then shut it down. Wait for the after-run cycle to complete (usually 30-90 seconds) to ensure the relay clicks off properly and the code does not return.