Powertrain, generic · Hybrid propulsion

P0A29 Hybrid/EV Battery Power Off Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0A29 is stored when the voltage on the hybrid battery power-off line sits above its plausible range for longer than allowed, which points to an open line pulled up internally or a short to a supply voltage. No manufacturer explains P0A29 publicly; GM merely names it as a keyword in a generic bulletin on terminal fit. The circuit itself is the hardwired disconnect path that patents describe beside the CAN crash message, and CARB 1968.2 requires monitoring of hybrid components relevant to emissions. Related: P0A28 for a signal too low, P0A27 when the contactors do not follow the command. A stuck-high line can keep the system from powering up or from shutting down correctly.

Likely causes

Open power-off line or unplugged connector
Power-off line shorted to battery voltage
Spread or corroded terminals at the connectors
Faulty input or driver stage in the control module

Symptoms

  • Hybrid system warning light
  • Vehicle does not reach ready mode
  • High-voltage system stays active after switching off

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

P0A27P0A28P0AA1P0AA4

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