Powertrain, generic (extended)

P2DC7 Starter/Generator Excitation Current

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2DC7 is the general fault for the excitation current of a starter/generator, meaning the DC current in the rotor field winding does not behave as commanded. Only wound-field machines have one. Valeo's 48 V belt starter generator, for instance, is a synchronous claw-pole machine; in such designs the stator gets three-phase current from an inverter, while a separate H-bridge drives direct current through brushes and slip rings into the rotor coil. Permanent-magnet starter/generators need no excitation, so the code does not apply to them. Regulator chips for wound-field alternators measure this current and can limit it, which is the basis for such checks. Switching the field off is also a safety tool against DC-link overvoltage. No manufacturer documents P2DC7 publicly. Low: P2DC8; high: P2DC9.

Likely causes

Worn brushes or contaminated slip rings on the rotor
Fault in the excitation H-bridge of the starter/generator electronics
Rotor field winding with interrupted turns or a short

Symptoms

  • Battery or charging warning lamp
  • Starter/generator stops charging and assisting
  • Stop-start disabled

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–2,000
Time1–4 h

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

Parts involved

starter generator excitation circuitstarter generatorstarter generator control module

Related codes

P2DC8P2DC9P2DCAP065B

References: ti.com, valeo.com, infineon.com.