P0904 code meaning
Gate Select Position Circuit A
Powertrain system Generic code P09xx codes Check engine light
What P0904 means
Circuit A of the gate select position sensor tells the control module of an automated manual gearbox where the shift mechanism stands in the select direction, i.e. which gate (for example 1-2, 3-4, 5-6 or reverse) is lined up. This generic circuit code sets when the module sees an electrical fault on that signal that is not covered by the more specific low, high or intermittent variants. No manufacturer documents the code publicly. Aisin AI and Isuzu patents describe such select stroke or select position sensors working next to an electric or hydraulic select actuator, and CARB requires circuit checks on transmission inputs of this kind. P0905 to P0908 are the siblings, P09A2 and P09A6 the same signal on circuits B and C. Without a valid gate signal the gearbox usually stops shifting or holds one gear.
P0904 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0904
- Check engine or transmission warning light on
- Gearbox stops shifting or stays in one gear
- Neutral indicator flashes or vehicle will not pull away
Common causes of P0904
- Most likelyLoose, corroded or water-damaged connector at the gate select sensor or actuator unit
- PossibleChafed or broken sensor wiring near the gearbox
- PossibleFaulty gate select position sensor (often integrated in the shift and select actuator)
- Less likelyFaulty sensor input or reference supply in the transmission control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Gate select position sensor aWiring harnessTCM
What each part of P0904 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9 | Area: transmission. |
| 04 | The exact fault in that area. |
What to do next
- Note P0904 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0904
What does P0904 mean?
P0904 means "Gate Select Position Circuit A". Circuit A of the gate select position sensor tells the control module of an automated manual gearbox where the shift mechanism stands in the select direction, i.e. It is a generic code, so it means the same on every make.
Is it safe to drive with P0904?
Drive gently and only to a workshop. With P0904 the car can go into limp mode (reduced power) to protect itself.
Will P0904 fail an emissions test?
Yes, it can. P0904 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0904 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P0904 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.