Case IH 15553 – Steering Control Unit: Open Circuit in Pump Drive Relay

The controlling module has detected an open circuit in the electrical path for the pump drive relay. This relay controls the auxiliary steering pump, which provides secondary or backup steering capability. An open circuit means there is a break in the wiring, a failed relay, or a poor connection preventing current from energizing the relay. This prevents the crucial backup steering system from engaging, potentially creating a significant safety issue if the primary steering fails.

• STX275
• STX325
• STX350
• STX375
• STX400
• STX425
• STX440
• STX450
• STX500
• STX550
• STX600
• Quadtrac

1. 1

   Visually inspect the wiring harness leading to the auxiliary steering pump and its associated relays for chafing, breaks, corrosion on connectors, or loose pins.

2. 2

   Inspect all fuses related to the steering and hydraulic systems in the main fuse panel.

3. 3

   Locate the auxiliary steering pump relay and swap it with an identical, known-good relay from a non-critical circuit (e.g., horn or work lights) to see if the fault clears.

4. 4

   Test the relay directly using a Digital Multimeter (DMM) for continuity across the coil (terminals 85 and 86) and switch operation (terminals 30 and 87) when 12V is applied.

5. 5

   Test the relay socket with the key on for 12V power at the coil supply, a good ground connection, and 12V at the main power supply terminal (30). If any of these are missing, use the tractor's electrical schematic to trace the specific wire and identify the break.

6. 6

   Check the wiring from the relay output (terminal 87) to the auxiliary steering pump motor for continuity.

1. 1

   De-energize the system

   Turn the tractor off and disconnect the battery to prevent electrical shorts.

2. 2

   Access components

   Based on your diagnostic findings, access the faulty component, whether it is the relay box, a section of the wiring harness, or the pump itself.

3. 3

   Replace or repair faulty component

   If the relay is faulty, replace it with a new OEM or equivalent part. If a wire is broken, repair it using a weatherproof splice and heat shrink tubing. If a connector is corroded, replace the connector and its pins.

4. 4

   Reassemble and test

   Reconnect the battery and all components. Start the tractor, clear the fault codes using a diagnostic tool or the onboard display, and operate the steering system to confirm the repair and ensure the fault code does not reappear.