P0904 Gate Select Position Circuit

P0904 indicates a gate select position circuit fault. The controller cannot reliably determine the selected gate position in the shift mechanism.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not adjust actuators blindly before confirming gate position sensor data and linkage alignment.

Symptoms of P0904

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0904

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Monitor gate select position data while moving through all gates and compare it with actual shifter or actuator movement.
Inspect position sensor reference voltage, signal, ground, connector fit, linkage alignment, actuator travel, and harness movement.
Check for companion gear shift position, actuator, or control error codes that show whether position data or motion is failing.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.