John Deere 191.08 – PTA / TCU / PTP: Transmission Output Speed Sensor, Speed at Channel 1 Lower Than at Channel 2.

This diagnostic trouble code is generated when the control software detects a frequency discrepancy between the two sensor output signals for the transmission output speed, specifically indicating that the speed reading at channel 1 is lower than the reading at channel 2. The machine will typically experience limited or no function of the transmission (or enter a protective limp mode) until the error is corrected.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6230
• 6330
• 6430
• 6420
• 8130
• 8230
• 8330
• 8530
• 8295R
• 8320R
• 7180
• 7280
• 7380
• 7480
• 7580
• 7780
• 7980

1. 1

   Verify Sensor Signals: Use a diagnostic tool (like John Deere Service ADVISOR) to compare the output signals of both channels of the transmission output speed sensor (B63 or B66) to ensure consistency.

2. 2

   Inspect Wiring and Connectors: Check the wiring harness and connectors associated with the sensor for signs of damage, corrosion, or disconnection. Look specifically for shorts to ground or open circuits on the channel 1 and channel 2 signal wires.

3. 3

   Test the Sensor: Use a multimeter to measure the frequencies and voltages of both sensor channels. If the sensor is providing inconsistent readings or low voltage on one channel, the sensor itself has failed.

4. 4

   Verify Control Unit Functionality: Ensure that the PTA/TCU control unit is correctly processing signals and check if a software payload update is available for the transmission controller.

5. 5

   Mechanical Inspection (IVT Specific): If the sensor and wiring test perfectly, use a borescope to inspect the internal transmission gear that the sensor reads from. A missing or chipped tooth on the tone ring/gear can cause erratic channel readings.

1. 1

   Locate the Sensor

   Locate the transmission output speed sensor (B63/B66) on the transmission housing (location varies by model, but it is typically mounted externally on the rear transmission case or near the output shaft).

2. 2

   Repair Wiring

   If the diagnostic checks revealed damaged wiring or corroded pins at the connector, repair or replace the faulty wiring harness section.

3. 3

   Replace the Sensor

   If the wiring is intact but the sensor failed the multimeter/frequency test, remove the retaining bolt, pull the old sensor from the transmission housing, and install a new OEM speed sensor.

4. 4

   Clear Codes and Calibrate

   After replacing the sensor or repairing the wiring, clear the 000191.08 fault code. For IVT transmissions, you must bring the transmission oil up to operating temperature and perform a transmission calibration procedure.