Case IH 3970 – Engine Control Module (ECM) / EDC (Electronic Diesel Control): After run relay high side driver circuit short to battery failure

The control module has detected a short to battery voltage on the high-side driver circuit that controls the 'after run' relay. This relay keeps the DEF/AdBlue system powered for a short period after the engine is shut off so the system can purge DEF fluid from the lines, preventing the fluid from freezing or crystallizing and damaging the pump.

• Steiger T4B
• Axial-Flow Combines 240 Series (7240, 8240, 9240)
• Magnum Tractors Tier 4B (Magnum 340, 380)
• Steiger Tractors Tier 4B

1. 1

   Inspect the After Run Relay in the engine fuse/relay box for an internal short circuit.

2. 2

   Check the 5 Amp mini fuse associated with the after-run relay circuit (Cavity 1 or 5 depending on the model).

3. 3

   Disconnect the ECM/EDC connector and the relay, then use a multimeter to check the high-side driver wire between the ECM and the relay socket for a short to battery positive.

4. 4

   Perform a visual inspection of the wiring harness between the ECM and the battery/relay block for chafing, melted insulation, or pinched wires.

1. 1

   Power Down

   Turn off the machine. Note that emergency re-starts are only enabled after the engine has been commanded to low idle, and the system allows 30 seconds of operation without power loss before reducing to low idle. Disconnect the battery before servicing the wiring.

2. 2

   Locate Components

   Access the engine fuse/relay box and locate the After Run Relay and its corresponding 5A fuse.

3. 3

   Replace Faulty Relay/Fuse

   If the relay fails a bench test (shorted internally) or the fuse is blown, replace them. Do not install a new fuse/relay until the wiring is verified.

4. 4

   Repair the Short

   If the multimeter test reveals a short to battery voltage in the harness, trace the wire from the relay block back to the ECM. Repair the chafed/shorted section of the wire using OEM-approved heat-shrink connectors.

5. 5

   Harness Replacement (If Necessary)

   If the short is deep within a main harness and cannot be isolated, the front frame/engine wire harness may need to be replaced. (Note: Some OEM replacement service harnesses do not include the after-run relay and fuse block, requiring you to transfer them).

6. 6

   Reassemble and Clear Codes

   Reconnect the battery, turn the key on, and use a diagnostic tool to clear DTC 6371 / 3970. Run the engine, shut it down, and listen for the DEF pump purge cycle to verify the after-run relay is functioning properly.