Powertrain, generic (extended)

P2D99 Starter/Generator Phase Y Current Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2D99 is stored when the phase Y current value of the starter/generator behaves in a way a real winding current cannot: sudden steps, dropouts to zero or noise between consecutive samples. The winding inductance smooths the true current, so such jumps implicate the measuring path. Only systems that actually sense phase Y can raise this code; GM's eAssist table, for example, lists current sensor checks for phases U and W alone. Mazda's ISG bulletin 01-004-25 confirms that a starter/generator may carry an X-Y-Z phase group. No manufacturer documents P2D99 publicly. Check the connector for corrosion and pin drag first, then the harness route near hot or moving parts. Steady counterparts: P2D93 (high), P2D96 (low), P2DC3 (circuit); X and Z intermittent: P2D98, P2D9A.

Likely causes

Corrosion or weak pin tension in the phase Y sensor connector
Harness damaged by heat from the exhaust side or by contact with moving parts
Phase Y current sensor producing a noisy or unstable signal

Symptoms

  • Sporadic hybrid or charging system warning
  • Recuperation occasionally interrupted

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 y current sensorwiring harnessstarter generator control module

Related codes

P2D98P2D9AP2D93P2D96P2DC3P2DC4

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