Powertrain, generic · Hybrid propulsion

P0A27 Hybrid/EV Battery Power Off Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0A27 covers the circuit that tells the high-voltage battery to drop off the bus, i.e. the command path that opens the main contactors at key-off, after a fault or after a crash signal. Patents describe such a path as a dedicated hardware line in addition to CAN, so the contactors open within milliseconds. The code sets when commanded and actual state disagree. Honda lists P0A27 as High Voltage Contactor Stays Activated on the 2012-15 Civic Hybrid, where it is one of the codes that call for replacing the motor power inverter. P0A28 and P0A29 are the low and high voltage faults of the same line. The driver may see a hybrid warning and the car may refuse to start or power down.

Likely causes

Contactor or its driver does not release when power-off is commanded
Internal fault in the inverter/power unit that controls the contactors (Honda Civic Hybrid)
Damaged wiring or loose terminal on the hardwired power-off line
Crash or emergency shutdown signal stored or still active

Symptoms

  • Hybrid system warning or check engine light
  • Vehicle will not enter ready mode or shuts down while driving
  • High-voltage system does not power down after key-off

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–3,000
Time1–6 h

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

Parts involved

hybrid battery power off circuitmain contactorsbms

Related codes

P0A28P0A29P0AA1P0AA4P0A0A

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