P0904: Gate Select Position Circuit A
What to do
Note carefully which gears you still have. On this kind of gearbox, losing gears in pairs — no first and second, but third and fourth fine — points at the mechanism that moves across the gate, which is a different part from the one that engages a gear. That distinction narrows the repair considerably.
What this code means
A fault in the sensor reporting the gate select position. This introduces the idea the whole P09xx block rests on, and it is worth setting out properly because it describes a genuinely different machine from the automatic gearboxes of P07xx.
An automated manual has no planetary gearsets and no clutch packs. It is an ordinary manual gearbox — the same shafts, the same synchronisers, the same H-pattern — with a robot working the lever instead of a driver. And because it is an H-pattern, changing gear takes two distinct motions, exactly as it does for a human hand:
- Select — moving across the gate to choose which plane of gears to work in, the sideways motion between 1/2, 3/4 and 5/6.
- Shift — moving along the gate to actually engage one, the fore-and-aft push or pull.
Gate select is the first of those, and it has its own actuator and its own position sensor. Anyone who has met the X and Y axes of a shift-by-wire selector under P0820 will recognise the arrangement immediately: same two-axis geometry, but here it is moving the gearbox rather than reading a driver.
The practical signature of a select fault is therefore losing gears in pairs or planes rather than individually — no first and no second, while third through sixth work perfectly. That pattern is the tell, and it is not something an automatic gearbox can produce.
Likely causes
Start here
- Faulty gate select position sensor · specialist
- Damaged transmission wiring harness · moderate
- Corroded transmission connector · moderate
Less common
- Faulty gate select actuator · specialist
Rare
- Faulty transmission control module · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0904.