Case IH 6912-03 - DEC – DEC: Transmission hydro motor speed sensor electrical circuit fault voltage above normal

The controller is receiving a voltage signal from the hydro motor speed sensor circuit that exceeds the maximum expected threshold. This is typically caused by the sensor's signal wire shorting to a power source (like a 5V reference or 12V battery voltage) or an open ground circuit causing the voltage to float high.

• MAGNUM AFS Connect
• Case IH Magnum Series Tractors (Magnum 280, 340, CVXDrive / Auto Command CVT)
• Case IH Axial-Flow Combines (7230, 8230, 9230, and 240 series)

1. 1

   Verify if the code is Active or Inactive. If inactive, it may indicate an intermittent wiring rub-through.

2. 2

   Inspect the wiring harness leading to the hydro motor speed sensor for pinched wires or areas where insulation has rubbed away, causing a short circuit to a high source.

3. 3

   Inspect the 2-pole female electrical connector at the sensor for moisture, corrosion, or pushed-out pins.

4. 4

   Disconnect the sensor and use a multimeter to check the signal wire for voltage with the key ON. If high voltage is present on the signal wire while disconnected, the short is in the harness. If the harness tests fine, the sensor has failed internally.

1. 1

   Locate the Sensor

   Locate the hydrostatic motor assembly on the transmission. The speed sensor is often protected by a specific bolt-on access cover.

2. 2

   Remove Access Cover

   Remove the bolts securing the hydro motor speed sensor access cover to gain clearance.

3. 3

   Remove the Sensor

   Disconnect the 2-pole wire connector. Remove the retaining hardware holding the speed sensor in the hydro motor housing and pull the sensor out.

4. 4

   Install New Sensor

   Lubricate the O-ring on the new speed sensor, insert it into the housing, and secure it with the retaining hardware.

5. 5

   Reconnect and Reassemble

   Plug in the electrical connector and reinstall the access cover.

6. 6

   Clear Codes

   Connect the Case IH EST (Electronic Service Tool) diagnostic laptop to clear the fault code. On some older ICU software versions, codes cannot be cleared via the cab keypad and require the EST tool.

7. 7

   Test Operation

   Test drive the machine to ensure the DEC registers the correct ground speed/motor speed and that the transmission shifts smoothly without throwing the pressure/speed code.