Cause
Faulty turbine speed sensor
The sensor reading the torque converter's turbine — the transmission's input speed — failed or reading erratically. It is one half of every ratio calculation the gearbox makes: input divided by output gives the ratio actually being achieved, and each gear has exactly one correct answer.
Which means a fault here does something unusual — it silences monitors rather than triggering them. Gear ratio checks, slip detection and torque converter lock-up monitoring all depend on this signal, so a car with a turbine speed fault often shows fewer transmission codes than it should. A slipping element can hide behind it, which is why a re-scan after the repair is worth asking for.
What the driver notices is lock-up. Without input speed the module cannot manage the torque converter clutch smoothly, so it is usually disabled — which shows as higher revs at a steady cruise, worse economy, or a shudder.
Two location-specific causes dominate. Transmission fluid wicks along the wires into the connector and bridges the terminals, and swarf collects on what is a magnetic sensor inside a gearbox. A heavily bearded sensor is reporting on the gearbox rather than on itself.
Ask where it is fitted before agreeing a price — external on some transmissions, behind the sump or valve body on others, for the same code.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (8)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0715 Input/Turbine Shaft Speed Sensor A Circuit Likely for this code High
- P0716 Input/Turbine Shaft Speed Sensor A Circuit Range/Performance Likely for this code High
- P0717 Input/Turbine Shaft Speed Sensor A Circuit No Signal Likely for this code High
- P0718 Input/Turbine Shaft Speed Sensor A Circuit Intermittent Likely for this code High
- P0730 Incorrect Gear Ratio Likely for this code High
- P076F Gear 7 Incorrect Ratio Moderate
- P07BF Input/Turbine Shaft Speed Sensor A Circuit Low Moderate
- P07C0 Input/Turbine Shaft Speed Sensor A Circuit High Moderate
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