Powertrain, generic · Transmission

P0904 Gate Select Position Circuit A

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

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.

Likely causes

Loose, corroded or water-damaged connector at the gate select sensor or actuator unit

Chafed or broken sensor wiring near the gearbox

Faulty gate select position sensor (often integrated in the shift and select actuator)

Faulty sensor input or reference supply in the transmission control module

Symptoms

Check engine or transmission warning light on
Gearbox stops shifting or stays in one gear
Neutral indicator flashes or vehicle will not pull away

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,500

Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

gate select position sensor awiring harnesstcm

References: law.cornell.edu, patents.google.com, patents.google.com.