Case IH 2586 (191.18) - DEC – UCM (Universal/User Control Module) or Transmission Electronic Control Module (ECM): Transmission Output Speed Sensor - critical air gap

The control module has detected that the physical distance (the "air gap") between the transmission output speed sensor (an inductive sensor) and the transmission ring gear/tone ring is out of specification. When the air gap becomes too large, the sensor cannot accurately read the passing gear teeth, resulting in a weak, erratic, or missing speed signal.

• MAXXUM T4E
• Case IH Puma series (165, 180, 195, 210, 225 CVX)
• Case IH Maxxum series
• Case IH Farmall series (95U, 105U, 115U Pro EP)

1. 1

   Check for related codes: Verify if any other error codes are being displayed. If other codes are present, diagnose those first, as they may be causing a cascading error.

2. 2

   Inspect the connector: Check the transmission output speed sensor connector (X-524 or X-309). Ensure the connector is fully seated, not damaged, the pins are in the correct position, and the fit is tight.

3. 3

   Test sensor resistance: Disconnect the sensor and use a multimeter to check the impedance across the terminals. A healthy sensor should read between 1000 to 1300 ohms, or up to 3.5k ohms.

4. 4

   Check for shorts: Ensure there is no continuity between the sensor terminals and the chassis ground.

1. 1

   Locate the sensor

   Find the transmission output speed sensor mounted on the exterior of the transmission case.

2. 2

   Remove and inspect

   Disconnect the electrical harness and remove the sensor. Inspect the tip of the sensor for physical damage, oil contamination, or metal debris, which can interfere with the magnetic field.

3. 3

   Verify the air gap

   If the sensor was loose or installed incorrectly, it must be refitted. Adjust the sensor's position to maintain the critical air gap. While exact specs vary by transmission, standard heavy-duty transmission speed sensors often require an air gap of approximately 0.060 to 0.090 inches (1.5 to 2.2 mm).

4. 4

   Replace the sensor

   If the sensor air gap is correct but the fault persists, or if the sensor fails the resistance test, replace the transmission output speed sensor with a new unit and install a new O-ring/seal.

5. 5

   Inspect the inductive ring

   If the fault is still present after replacing the sensor and verifying the wiring, there is likely a mechanical fault with the speed sensor inductive ring (tone ring) inside the transmission, which will require internal transmission inspection.

6. 6

   Clear codes

   Once the repair is complete, clear the error code via the instrument cluster or diagnostic tool and test the tractor for normal operation.