Case IH 1883-03 - DEC – DEC: Rear PTO shaft speed sensor electrical circuit fault voltage above normal

A "voltage above normal" fault for a sensor typically indicates an open circuit (a broken wire or disconnected plug) or a short to a power source (short to battery). The controller is seeing a return voltage signal that exceeds the maximum expected operating threshold (usually >4.5V or 5V on a 5V reference circuit), meaning the sensor is not pulling the voltage down as it should.

• MAGNUM AFS Connect
• Magnum Series
• MX Series
• MX285
• TG Series
• CS Series
• CS 94

1. 1

   Visual Inspection: Check the wiring harness leading to the PTO shaft speed sensor (typically located ahead of and to the right of the rear PTO shaft). Look for chafed wires or disconnected plugs.

2. 2

   Continuity Check (Signal & Power): Check the continuity from the controller connector (e.g., Pin 10 of connector C056) to Pin A of the sensor connector (e.g., C145).

3. 3

   Continuity Check (Ground): Check the continuity from Pin B of the sensor connector to the chassis ground. An open ground will cause a "voltage above normal" code.

4. 4

   Sensor Resistance Check: Test the function of the speed sensor itself using a multimeter. A healthy Case IH PTO speed sensor should have a resistance of approximately 3 K ohms.

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the negative battery terminal to prevent electrical spikes.

2. 2

   Access the Sensor

   Locate the rear PTO shaft speed sensor at the rear housing of the PTO assembly.

3. 3

   Test the Harness

   Disconnect the sensor. Using a multimeter, verify that the 5V reference and ground are present on the harness side when the key is turned ON. If the ground is missing, trace the harness back to repair the broken wire.

4. 4

   Test the Sensor

   Measure the resistance across the pins of the sensor. If it reads open (infinite resistance) or significantly deviates from 3 K ohms, the sensor has failed internally.

5. 5

   Replace the Sensor

   Unbolt the retaining collar/bolt holding the sensor in the housing. Remove the old sensor and O-ring.

6. 6

   Install New Parts

   Lubricate the new O-ring with clean hydraulic/transmission fluid. Insert the new sensor, tighten the retaining bolt, and plug in the electrical connector.

7. 7

   Clear Codes

   Reconnect the battery, power up the tractor, and use the diagnostic menu or a scan tool to clear the DEC/UCM fault codes. Run the PTO to verify the speed registers on the dash.