P0A28Hybrid/EV Battery Power Off Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Hybrid system warning light
- Vehicle does not reach ready mode
- Electric drive disabled, engine runs constantly
- Likely causes
- LikelyPower-off signal line shorted to ground
- PossiblePoor terminal fit or corrosion at the battery or control module connector
- PossibleMissing supply or blown fuse feeding the power-off circuit
- RareFaulty driver stage in the battery or hybrid control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.