Powertrain, generic (extended)

P2D9B Starter/Generator Phase U Current Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2D9B concerns phase U, the first phase of the starter/generator's main U-V-W group, when its current signal is unsteady rather than permanently out of range. GM's eAssist system, whose belt-driven machine appears in its tables as drive motor A, shows how a manufacturer separates hard limits from short events: the U sensor fails high or low beyond 440 A in either direction within 41.6 ms, while a fast, repeated overcurrent is handled by switching the inverter off for one 2.08 ms loop, counting the event and re-enabling, with the code following the third count. No manufacturer documents P2D9B itself publicly. Typical causes are a marginal plug contact, a damaged lead or a failing sensor. V and W intermittent: P2D9C, P2D9D; X to Z: P2D98 to P2D9A.

Likely causes

Marginal contact in the phase U sensor connector
Phase U sensor lead with damaged insulation or a partly broken strand
Phase U current sensor beginning to fail

Symptoms

  • Intermittent warning lamp, sometimes only after several trips
  • Sudden loss of electric assist, returning after a restart

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,000
Time0.5–5 h

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

Parts involved

starter generator phase u current sensorwiring harnessstarter generator control module

Related codes

P2D9CP2D9DP2D98P0BE7P0BE8P0C01

References: gsi.ext.gm.com, static.nhtsa.gov.