Case IH 15268 - AST – AST Steering Valve Controller: AST: Steering valve controller failure - Software detected SPI communication queue full

A software-level buffer overflow within the steering valve controller where the SPI communication queue is full, meaning the controller's internal software is receiving data faster than it can process it or a firmware glitch has caused the data buffer to lock up, preventing safe auto-guidance steering commands.

• MAXXUM T4E
• VESTRUM CVX
• Case IH Mid-Range (MR) Stage V tractors
• Case IH Maxxum
• Case IH Puma
• Case IH Farmall

1. 1

   Perform a hard key cycle (turn off, wait for ECU main relays to click off, and restart) to see if the SPI buffer clears

2. 2

   Check the current firmware version of the AST Steering Valve Controller using the CNH Electronic Service Tool (EST)

3. 3

   Inspect the wiring harness connecting to the steering valve controller for moisture ingress, corrosion, or loose pins

1. 1

   Cycle Ignition

   Turn off the machine and let the CAN bus go to sleep to attempt a module reset.

2. 2

   Reflash the Controller

   If the code remains active or is frequently intermittent, use the CNH EST to flash the AST Steering Valve Controller with the latest software calibration file.

3. 3

   Clean Connections

   Disconnect the main harness at the steering valve. Clean the pins with electronic contact cleaner, ensure no pins are pushed back, apply a light coat of dielectric grease, and reconnect.

4. 4

   Clear and Retest

   Clear the fault stack using the EST. Test drive the tractor and engage the AST auto-guidance system to verify the steering valve responds without throwing the code.

5. 5

   Replace the Valve

   If the software is up to date, the wiring is intact, and the code persists, the internal micro-controller on the steering valve has suffered a hardware failure. The steering valve assembly must be replaced and recalibrated.