Case IH 3969 – Engine ECU: After run relay high side ECU driver circuit over temperature failure.

The Engine Control Unit (ECU) has detected that the internal driver circuit responsible for supplying voltage (the "high side") to the After Run Relay has exceeded its maximum safe operating temperature. This condition is typically caused by excessive current draw on the circuit, which usually points to a short to ground in the wiring harness between the ECU and the relay, or an internally shorted relay coil drawing too much amperage.

• Steiger T4B
• 240 Series Axial-Flow Combines
• 7240
• 8240
• 9240

1. 1

   Visually inspect the After Run Relay, socket, and surrounding wiring for physical signs of melting, heat damage, or corrosion.

2. 2

   Remove the After Run Relay and use a multimeter to test the resistance across the relay coil pins. An abnormally low resistance indicates an internal short in the relay.

3. 3

   With the battery disconnected and the ECU unplugged, test the high-side driver wire running from the Engine ECU to the relay socket for a short to ground.

4. 4

   Inspect the connector at the Engine ECU for any signs of heat damage, pushed-out pins, or corrosion that could cause high resistance or shorting.

1. 1

   Disconnect Power

   Turn off the combine and disconnect the negative battery cable to prevent electrical spikes or further damage to the ECU.

2. 2

   Access the Relay

   Locate the engine power distribution center / relay box and remove the After Run Relay.

3. 3

   Repair Wiring (If Applicable)

   If a short to ground was found in the wiring harness during diagnostics, repair the chafed/damaged wire using proper soldering and heat-shrink techniques, or replace the affected harness section.

4. 4

   Replace the Relay

   If the relay coil was found to be shorted or if the relay shows signs of heat damage, install a new OEM After Run Relay into the socket.

5. 5

   Reassemble and Reconnect

   Ensure all ECU connectors are securely seated and reconnect the battery.

6. 6

   Clear Codes and Test

   Connect a diagnostic tool to clear the inactive DTC 8271 / 3969. Start the engine, let it run briefly, and then shut it down. Monitor the machine to ensure the after-run cycle completes successfully without the ECU logging the over-temperature fault again.