Powertrain, generic (extended)

P2DC4 Starter/Generator Phase Y Current Sensor Circuit Range/Performance

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

P2DC4 says the phase Y current reading of the starter/generator is inside its electrical limits but fails a plausibility test. One way to test it is an energy balance: the power drawn or delivered on the phase side must match the current on the DC side. GM's eAssist machine compares the sum derived from its phase sensors with the DC-DC converter input and battery pack current; a gap above 40 A in 90 of 96 checks, run every 2.08 ms, sets a two-trip Type B code, and current control then continues without the sensors. GM measures U and W only, so this is an analogue, not P2DC4 itself, which no manufacturer documents publicly. A sensor with a gain error or a drifting zero is the usual suspect. Circuit: P2DC3; X and Z range: P2DC2, P2DC6.

Likely causes

Phase Y current sensor reading consistently too high or too low

Zero offset of the phase Y sensor drifted

Comparison value wrong because the DC-side current measurement is faulty

Symptoms

Warning lamp after two trips with the fault
Noticeably weaker boost and smoother but slower restarts

Repair estimate

DifficultyHardWorkshop job

Parts and labour€150–2,000

Time0.5–4 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

References: gsi.ext.gm.com, law.cornell.edu.