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P077B Severity
Identifying an OBD code is just the start of a complete diagnostic routine. Most trouble codes are caused by a sensor reporting a value that is out of range. Just replacing a sensor may not fix underlying issues. Be sure to understand the code, the part or system in your car that the code refers to, and the risks of delaying professional repair.
Proper diagnosis will save you time and money on unnecessary repairs.
Urgent codes indicate immediate action is necessary. These are urgent and significant malfunctions that can cause severe damage to the vehicle or harm the driver and passengers.
The Output Speed Sensor tells the Transmission Control Module (TCM) how fast the output shaft of the transmission is spinning so it can verify the correct gear is engaged. Some manufacturers add a second Output Shaft Speed Sensor to enable the TCM to determine what direction the shaft is rotating. When the TCM receives an implausible signal from these sensors, the engine control module (PCM) or Hybrid Control Module will set code P077B.
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OBD-II Code Transmission may not shift properly is defined as a Output Speed Sensor Circuit - Direction Error
The Output Speed Sensor tells the Transmission Control Module (TCM) how fast the output shaft of the transmission is spinning so it can verify the correct gear is engaged. Some manufacturers add a second Output Shaft Speed Sensor to enable the TCM to determine what direction the shaft is rotating. When the TCM receives an implausible signal from these sensors, the engine control module (PCM) or Hybrid Control Module will set code P077B.