Case IH 161-03 - DEC – Transmission Electronic Control Unit (TECU / TCU): Transmission Input Shaft Speed Sensor - Voltage Above Normal or Shorted to High Source

The control module has detected a short circuit to power (B+) in the Transmission Input Shaft Speed Sensor's wiring for a sustained period (usually 5 seconds or more).

• MAGNUM AFS Connect
• Magnum Series (e.g., 180, 200, 225, 250, 340, 7100/7200/8900 series)
• Maxxum Series (e.g., 100, 115, 125, 140)
• Steiger / Quadtrac Series (e.g., 435, 535)
• Puma Series
• Case wheel loaders (e.g., 521D)

1. 1

   Visually inspect the transmission wiring harness and the sensor connector for rubbed-through insulation, corrosion, bent pins, or moisture ingress.

2. 2

   With the key ON, disconnect the sensor and use a multimeter to measure the voltage at the harness connector. If full battery voltage is present on the signal return wire, the harness is shorted to a high power source.

3. 3

   Remove the sensor and inspect the magnetic pickup tip for adherence of iron particles, metal shavings, or physical scratches that could skew readings.

4. 4

   Measure the resistance across the sensor pins to verify it is within the expected OEM specification to rule out an internal short.

1. 1

   Power Down

   Turn the key OFF and disconnect the battery ground to prevent further electrical damage.

2. 2

   Harness Repair

   If a short is found, trace the sensor wiring back to the TECU. Locate the chafed wire that is shorting to a power wire. Repair the damaged section using weather-sealed splice connectors, or replace the transmission harness section if the damage is extensive.

3. 3

   Sensor Replacement

   If the sensor is internally shorted, locate the input shaft speed sensor (usually threaded into the top or side of the transmission main case, or on the PTO cover). Disconnect the 3-wire electrical connector and unthread the old sensor. Transfer any spacers/shims to the new sensor if applicable. Apply liquid gasket (e.g., LG-5) to the threaded part if required, then thread the new sensor into the housing and tighten to OEM torque specs.

4. 4

   Reassembly

   Reconnect the electrical connector, reconnect the battery, and clear the inactive fault codes via the tractor's diagnostic display. Test drive to ensure the transmission shifts smoothly and the speedometer registers correctly.