Case IH 191-01 - DEC – Transmission Control Module (TCM) or Instrumentation Controller: Transmission Output Speed Sensor (TOSS) / Vehicle Speed Sensor (VSS) Data Valid But Below Normal Operational Range - Most Severe Level

The controller is not detecting a valid signal from the transmission output speed sensor while the vehicle is moving, or the signal has dropped below the minimum expected threshold. In some configurations, this code can also be triggered simply as a result of the vehicle reaching an over-speed condition (if over-speed parameters are enabled), rather than an actual hardware failure.

• MAGNUM AFS Connect
• Magnum 180
• Magnum 200
• Magnum 225
• Magnum 340
• Maxxum series
• Puma series
• Farmall 60A
• Farmall 95U
• Farmall 105U
• Farmall 115U
• Combine 7010
• Combine 7120
• Combine 8010
• Combine 8120
• Combine 9010
• Combine 9120
• Combine AFX8010
• Sugar Cane Harvester A8800

1. 1

   Check Over-Speed Parameters: Verify if the customer has requested to turn on vehicle over-speed notices. If the vehicle simply exceeded the maximum speed limit, the 191-01 fault is logged due to OBD requirements and should not be diagnosed as a hardware issue.

2. 2

   Service Tool Monitoring: Connect the electronic service tool to the tractor. Go to the monitor screen, select 'change parameter selections,' and view 'inst trans output speed' to display the sensor output in RPM while the machine is moving.

3. 3

   Visual Inspection: Inspect the wiring harness, the sensor connector, and the tone ring of the VSS/TOSS. Look for corroded pins, burnt circuits, or weak relays, which are common causes of TCM communication losses.

4. 4

   Compare Sensors (If Applicable): If the transmission utilizes two output speed sensors (TOS #1 and TOS #2), use the TCM to compare the two signals to check if one is invalid or if they have been connected backwards.

1. 1

   Secure the Machine

   Park the machine on a level surface, engage the parking brake, and turn off the engine.

2. 2

   Locate the Sensor

   Locate the Transmission Output Speed Sensor on the transmission housing or rear axle housing (location varies by model).

3. 3

   Disconnect Wiring

   Carefully unplug the 4-way electrical connector from the sensor.

4. 4

   Remove the Sensor

   Remove the retaining bolt/nut and pull the sensor out of the housing. Be prepared to catch a small amount of transmission fluid.

5. 5

   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 hardware.

6. 6

   Reconnect and Clear Codes

   Reconnect the wiring harness. Use the service tool to clear the 191-01 fault code from the TCM/Instrumentation Controller.

7. 7

   Test Drive

   Operate the machine and monitor the transmission output speed via the service tool to ensure the signal is steady and the code does not return.