Case IH 191-03 - DEC – Transmission Control Module (TCM) or Engine Control Module (ECM): Transmission Output Shaft Speed - Voltage Above Normal, or Shorted to High Source

The control module is detecting an electrical voltage signal from the Transmission Output Speed Sensor (TOSS) circuit that exceeds the normal operating range (typically above the 4.75V - 5.25V threshold). This condition usually indicates that the sensor's signal wire is shorted to a power source (battery voltage), or the sensor itself has suffered an internal short circuit.

• MAGNUM AFS Connect
• Magnum
• Steiger
• Puma
• Maxxum
• Optum
• Axial-Flow

1. 1

   Visually inspect the Transmission Output Speed Sensor (TOSS) and its wiring harness for physical damage, melted wires, or heavy contamination.

2. 2

   Disconnect the sensor and inspect the connector pins for corrosion, moisture, or bent terminals.

3. 3

   Perform a voltage test on the harness side (key ON, engine OFF) to check if the signal wire reads battery voltage (12V) instead of the standard 5V reference, indicating a short to power.

4. 4

   Test the sensor's internal resistance to check for an internal short circuit.

5. 5

   If the sensor tests fine, disconnect the harness at the TCM/ECM and check for continuity between the signal wire and power supply wires to isolate the short in the harness.

1. 1

   Power Down

   Turn off the machine, remove the key, and turn the battery disconnect switch to the OFF position to prevent electrical spikes.

2. 2

   Access the Sensor

   Locate the Transmission Output Speed Sensor on the transmission housing. Clean the area around the sensor to prevent dirt from falling into the transmission.

3. 3

   Remove the Sensor

   Disconnect the electrical connector. Remove the retaining bolt(s) holding the sensor in place. Carefully pull the sensor straight out of the housing.

4. 4

   Install the New Sensor

   Lubricate the O-ring on the new sensor with clean transmission fluid. Insert the sensor into the housing and tighten the retaining bolt to the OEM torque specification.

5. 5

   Harness Repair (If Applicable)

   If the diagnostic checks revealed a short in the wiring harness rather than a faulty sensor, locate the chafed or melted section of the wire. Splice in a new section of wire using weather-sealed heat-shrink connectors, or replace the affected harness section.

6. 6

   Reassemble and Test

   Reconnect the sensor harness. Turn the battery disconnect switch back on.

7. 7

   Clear Codes

   Connect a diagnostic tool (such as the CNH Electronic Service Tool) to clear the inactive 191-03 fault code. Test drive the machine to ensure the transmission shifts correctly and the speedometer registers accurately without the code returning.