P077B — Output Shaft Speed Sensor Circuit - Direction Error
The TCM reads a direction from the output shaft speed sensor that contradicts the commanded gear — for example reverse direction while drive is engaged, or forward direction while reverse is engaged. Either the sensor wiring is swapped, the sensor is wrong, or the gear actually engaged is not the one commanded.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Output shaft speed sensor
- Transmission
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Sensor wiring swapped after service
- Wrong sensor part installed
Possible symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Diagnostic notes
- The malfunction indicator lamp may illuminate
Related codes
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.