P2D9BStarter/Generator Phase U Current Circuit Intermittent/Erratic
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Intermittent warning lamp, sometimes only after several trips
- Sudden loss of electric assist, returning after a restart
- Likely causes
- LikelyMarginal contact in the phase U sensor connector
- PossiblePhase U sensor lead with damaged insulation or a partly broken strand
- RarePhase U current sensor beginning to fail
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.