The input and output speeds do not match the ratio of the selected gear. The driver may notice slipping, flare between shifts or a stuck gear.
Likely causes, most common first
- Low or burnt transmission fluid
- Faulty shift solenoid or valve body
- Worn clutches inside the transmission
- Faulty speed sensor
Parts usually involved
- Transmission fluid
- Shift solenoids
- Valve body
- Speed sensors
Test before you replace
Check fluid level and condition, then compare input and output speed live and check line pressure.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.