Powertrain, generic · Transmission

P09A4 Gate Select Position Circuit B Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Set when the gate select signal on circuit B stays below its lowest valid value for longer than a calibrated time. Likely causes are a signal line shorted to ground, a lost sensor supply or an internal sensor short; with potentiometer sensors like the select position sensor in an Isuzu patent, an open signal wire often reads low too. No manufacturer documents this code publicly, nor whether B is a second track or another sensor. CARB requires out-of-range checks on such inputs. P09A5 is the opposite fault, P09A2 the general circuit fault, P0906 and P09A8 the low faults of circuits A and C. If A and B are both low, look for a shared supply or ground.

Likely causes

Signal wire of circuit B chafed through and shorted to ground
Sensor reference supply interrupted or shorted
Internal short or broken wiper in the select sensor
Faulty input stage in the transmission control module

Symptoms

  • Check engine or transmission warning light on
  • Gear changes blocked or limited to a few gears
  • 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 bwiring harnesstcm

Related codes

P09A2P09A3P09A5P0906P09A8

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