Powertrain, generic (extended)

P2DCC Starter/Generator Position Sensor Correlation

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2DCC reports that the rotor position or speed the starter/generator derives from its own sensor disagrees with an independent reference. For a belt-driven machine the natural reference is the crankshaft: engine speed times the pulley ratio has to match machine speed. GM's eAssist runs this comparison under the drive motor performance code P0A90: more than 1,000 rpm between machine and ECM speed for 1.5 s within 2 s sets it as a one-trip Type A, while gaps above 500 rpm are counted over two key cycles. GM also watches the resolver for a tracking error above 5 degrees. A slipping belt can therefore look like a sensor fault. No manufacturer documents P2DCC publicly. Lacking a reliable angle, the controller usually stops assist and auto-start; CARB asks that such generator faults be detected.

Likely causes

Slipping drive belt or weak belt tensioner
Rotor position sensor degraded or shifted
Faulty engine speed reference from the crankshaft sensor or its CAN signal

Symptoms

  • Start-stop and electric assist disabled
  • Belt squeal or engine restart via 12 V starter instead
  • Check engine light

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–2,000
Time0.5–4 h

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

Parts involved

starter generator position sensorstarter generator control module

Related codes

P0A90P2BA3P0A40P2DCBP2CF9

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