Powertrain, generic (extended)

P2D9D Starter/Generator Phase W Current Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2D9D covers phase W of the starter/generator when its current signal flickers or drops out for moments. The W sensor is one of the two that GM's eAssist belt machine monitors. GM's checks there look at solid failures: below -440 A or above 440 A for 41.6 ms, Type B, and a learned zero offset beyond 30 A while the inverter is off. A brief glitch that never crosses such limits is what an intermittent code is meant to catch. No manufacturer documents P2D9D publicly. Hall sensors around the phase conductors deliver a voltage that follows the current, so a drifting reference, moisture or a cracked solder joint in the electronics can make the reading jump. Steady W faults belong to other codes; U and V intermittent: P2D9B, P2D9C.

Likely causes

Moisture inside the starter/generator electronics
Cracked solder joint in the sensor path after many heat cycles
Poor contact in the phase W sensor connector

Symptoms

  • Warning lamp that shows up mostly when the engine is hot or the weather is wet
  • Charging through the starter/generator briefly 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 w current sensorwiring harnessstarter generator control module

Related codes

P2D9BP2D9CP2D9AP0BEEP0BEFP0BF0

References: gsi.ext.gm.com, powersystemsdesign.com.