Powertrain, generic

P0EF9 Battery Charger A Input Voltage Sensor B Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P0EF9 means the signal of input voltage sensor B in charger A has fallen below its valid range. No manufacturer documents P0EF9 publicly. GM's 2019 plug-in hybrid summary fails the matching sensor A code P0D3F when the duty cycle is 8 % or less but above zero, or stuck at 100 %, in at least 30 samples out of a window of 40 (Type B); a short to ground or a missing sensor supply produce that picture. Note that low refers to the measurement signal and not to a weak mains supply, which manufacturers report with input voltage too low codes such as P0D27. Because the charger cannot verify the incoming voltage, it does not begin AC charging. The high-side counterpart is P0EFA, the general circuit code P0EF7.

Likely causes

Internal fault of the charger measuring stage
Sensor signal shorted to ground
Missing supply voltage of the sensing circuit

Symptoms

  • AC charging refused
  • Charging fault message right after plugging in
  • DC fast charging usually still possible

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–2,500
Time0.5–4 h

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

Parts involved

battery charger a input voltage sensor bwiring harnesson board charger

Related codes

P0EFAP0EF7P0EF8P0D3FP0D27

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