Case IH 191-00 - DEC – Transmission Electronic Control Module (ECM / TCU): Transmission Output Shaft Speed - Data Valid But Above Normal Operational Range - Most Severe Level

The control module is receiving a signal from the Transmission Output Speed (TOS) sensor that is readable (valid) but indicates an RPM or speed value that is excessively high and outside the normal operating parameters. This often points to an erratic, intermittent, or incorrect signal caused by a failing sensor, electrical noise, or a wiring issue.

• MAGNUM AFS Connect
• Magnum series (Tier 4A/4B, PST, CVT, SmartTrax)
• Puma series
• Maxxum series
• Farmall series (95U, 105U, 115U Pro EP)
• B115B backhoe loaders

1. 1

   Connect the electronic service tool to the tractor, navigate to the monitor screen, and select the parameters for 'inst ground speed - wheel' and 'inst trans output speed' to monitor live data.

2. 2

   Compare the live data signals between TOS sensor #1 and TOS sensor #2 to see if one of the two signals is erratic, dropping out, or reading significantly higher than the other.

3. 3

   Inspect the transmission output speed sensor wiring harness for physical damage, corrosion at the connector, or shorts that could introduce input noise into the circuit.

1. 1

   Locate the Sensor

   The transmission output speed sensor is typically located on the rear axle housing or the transmission case.

2. 2

   Clean the Area

   Thoroughly clean the area around the sensor to prevent dirt or debris from entering the transmission/axle housing.

3. 3

   Disconnect

   Unplug the electrical connector from the speed sensor.

4. 4

   Remove Hardware

   Remove the retaining hardware (often a stud bolt and nut) securing the sensor to the housing.

5. 5

   Extract the Sensor

   Carefully pull the sensor out of the housing.

6. 6

   Replace O-Ring

   Always remove and discard the old O-ring. Lubricate a new O-ring with clean transmission/hydraulic oil and install it on the new sensor.

7. 7

   Install

   Insert the new sensor into the housing, install the retaining bushing/stud bolt, and tighten the nut to OEM torque specifications.

8. 8

   Reconnect and Clear

   Reconnect the electrical harness, clear the 191-00 fault code using the service tool, and test drive the machine while monitoring the TOS RPM data to verify the repair.