Powertrain, generic · Hybrid propulsion

P0A28 Hybrid/EV Battery Power Off Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The control unit watches the voltage on the line that commands the high-voltage battery to disconnect. P0A28 sets when that signal stays below its valid window for a calibrated time, typical of a short to ground or a lost supply on the line. No manufacturer documents P0A28 publicly; GM only lists it as a search keyword in a general pin-fit bulletin. Patents show the power-off path as a hardwired line next to CAN that opens the contactors within milliseconds; CARB requires hybrid components that can affect emissions to be monitored. P0A29 is the opposite fault, P0A27 a mismatch between command and contactor state. Expect a hybrid warning and, depending on strategy, no ready mode.

Likely causes

Power-off signal line shorted to ground
Poor terminal fit or corrosion at the battery or control module connector
Missing supply or blown fuse feeding the power-off circuit
Faulty driver stage in the battery or hybrid control module

Symptoms

  • Hybrid system warning light
  • Vehicle does not reach ready mode
  • Electric drive disabled, engine runs constantly

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,500
Time1–5 h

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

Parts involved

hybrid battery power off circuitwiring harnessbms

Related codes

P0A27P0A29P0AA1P0AA4

References: law.cornell.edu, patents.google.com, static.nhtsa.gov.