Case IH 3437 – Engine Control Unit (ECU): After run relay low side driver circuit short to ground failure

The Engine Control Module (ECM) has detected a 'short to ground' on the low-side driver circuit that controls the After Run Relay. This causes the relay to stay energized continuously, which can drain the battery or prevent the ECU from shutting down properly.

• Axial-Flow Combines 240 Series
• Steiger Tractors
• Magnum Tractors

1. 1

   Locate the Relay: Find the After Run Relay in the main electrical fuse/relay distribution box (often designated as C351 in Steiger models).

2. 2

   Visual Inspection: Remove the relay and inspect the socket terminals for corrosion, melting, or pushed-out pins.

3. 3

   Circuit Testing: Disconnect the harness connector at the Engine ECU. Using a digital multimeter, check for continuity to ground on the low-side driver control wire (the wire running from the ECU connector to the relay socket). If continuity to ground is present while both ends are disconnected, the wiring harness is shorted to the chassis.

4. 4

   Relay Testing: Test the relay coil for an internal short circuit that could be pulling excessive current and causing the ECU driver to fault.

1. 1

   De-energize the System

   Turn off the main battery disconnect switch to ensure the electrical system is completely powered down.

2. 2

   Harness Repair

   If the multimeter test revealed a short to ground in the wiring, trace the harness from the relay panel to the Engine ECU. Look for pinch points, areas where the harness rubs against the frame, or melted insulation.

3. 3

   Splice/Replace

   Repair the damaged wire by splicing in a new section using OEM-approved weather-sealed connectors, or replace the affected harness section entirely.

4. 4

   Relay Replacement

   If the wiring tests good but the relay coil is internally shorted or degraded, replace the After Run Relay.

5. 5

   Verification

   Reconnect the ECU and install the new/tested relay. Turn on the battery disconnect, turn the ignition key ON and then OFF, and wait for the after-run cycle to complete to verify the relay clicks off properly. Clear the fault codes using the diagnostic service tool.