Cause
Faulty gate select position sensor
On an automated manual transmission, the sensor reporting where the actuator has moved across the gate — the side-to-side movement that chooses which pair of gears is available, as distinct from the fore-and-aft movement that engages one of them. Picturing a manual gear lever makes the split obvious, and the two axes have separate actuators, separate sensors and separate codes.
The transmission cannot shift without this reading and will not try. Selecting the wrong plane and then engaging would attempt a gear the driver did not ask for, so a module that has lost confidence in gate position refuses to change gear at all, and typically leaves the vehicle in whatever gear it was in or in neutral. The complaint is therefore a car that will not shift rather than one that shifts badly.
Circuit and performance codes want different work. Low, high and intermittent are wiring — and this harness runs on the gearbox itself, through heat, vibration and road spray, so a chafed loom or a wet connector is the likeliest finding. A range or performance code with a sound circuit is usually mechanical: a sensor that has shifted on its mounting, or an actuator no longer reaching its stops, so the reading is honest and the travel is not what the module expects.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (5)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0904 Gate Select Position Circuit A Likely for this code High
- P0905 Gate Select Position Circuit A Range/Performance Likely for this code High
- P0906 Gate Select Position Circuit A Low Likely for this code High
- P0907 Gate Select Position Circuit A High Likely for this code High
- P0908 Gate Select Position Circuit A Intermittent Likely for this code High
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