Powertrain, generic · Transmission

P09A8 Gate Select Position Circuit C Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The module stores this code when the gate select signal on circuit C remains below its valid range for a calibrated time. Common triggers are a signal wire shorted to ground, a missing sensor supply or an internal sensor fault; depending on the sensor type, a broken signal wire can read low as well. No manufacturer documents this code publicly or explains what circuit C measures. Patents from Isuzu and Aisin AI show the select sensor as the feedback the module needs to line up the right gate. CARB requires out-of-range checks on such inputs. P09A9 is the high counterpart, P09A6 the general C fault, P0906 and P09A4 the low faults of A and B.

Likely causes

Signal wire of circuit C shorted to ground
Sensor supply for circuit C missing or pulled down
Internal short in the sensor delivering signal C
Faulty input stage in the transmission control module

Symptoms

  • Check engine or transmission warning light on
  • Gearbox holds one gear or drops to neutral
  • Transmission warning message in the instrument cluster

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,500
Time0.5–4 h

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

Parts involved

gate select position sensor cwiring harnesstcm

Related codes

P09A6P09A7P09A9P0906P09A4

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