Case IH 2678 – ZDC (Transmission Controller): Transmission output shaft speed sensor measured speed not corresponding with transmission output shaft speed CAN signal from ZDC

There is a data mismatch where the physical transmission output shaft speed sensor is sending a hardwired speed reading that conflicts with the speed data being broadcast over the CAN bus network by the transmission controller. This discrepancy typically points to a failing speed sensor (erratic pulse frequency), damaged sensor wiring, or a CAN bus communication error preventing the correct speed data from being shared across the tractor's network.

• Steiger T4B
• Puma 150
• Puma 165
• Puma 185
• Puma 200
• Puma 220
• Puma 240
• Magnum 180
• Magnum 200
• Magnum 220
• Magnum 240
• Magnum 250
• Magnum 280
• Magnum 310
• Magnum 340
• Magnum 380
• Optum 250
• Optum 270
• Optum 300
• Steiger Series (CVT)

1. 1

   Visual Inspection: Inspect the transmission output shaft speed sensor wiring harness and connector for chafing, corrosion, or loose pins (a common cause of erratic sensor readings).

2. 2

   CAN Bus Network Test: Check the CAN bus communication lines between the ZDC and the VCM for continuity and proper voltage (CAN High / CAN Low) to rule out a network failure.

3. 3

   Sensor Testing: Test the sensor's resistance and voltage output according to the service manual specifications to see if the internal magnetic induction/Hall effect circuit has failed.

4. 4

   Mechanical Inspection: If the sensor tests fine, remove it and inspect the transmission output shaft tone ring/gear through the sensor port for damage, metal shavings, or debris that could disrupt the magnetic pulse.

1. 1

   Safely park the tractor on level ground, engage the parking brake, turn off the engine, and disconnect the battery to prevent electrical shorts.

2. 2

   Locate the transmission output shaft speed sensor on the exterior of the transmission housing.

3. 3

   Depress the locking tab and disconnect the multi-pin weather-pack electrical connector from the sensor.

4. 4

   Remove the retaining bolt(s) securing the sensor to the transmission casing.

5. 5

   Carefully twist and pull the sensor to extract it from the housing. Have a rag ready, as a small amount of transmission fluid may leak.

6. 6

   Clean the mounting port on the transmission housing, ensuring no dirt enters the transmission.

7. 7

   Lubricate the heavy-duty synthetic rubber O-ring on the new sensor with clean transmission fluid.

8. 8

   Insert the new sensor into the housing and torque the retaining bolt to OEM specifications.

9. 9

   Reconnect the electrical connector, ensuring it clicks into place.

10. 10

    Reconnect the battery, clear the fault codes using the Case IH Electronic Service Tool (EST), and perform a test drive to verify the speedometer reads correctly and the transmission shifts smoothly without limp-mode defaults.