P0A9CHybrid/EV Battery Temperature Sensor A Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- This is a plausibility check: the reading of temperature sensor A is compared with the other sensors in the same pack, which should agree within a few degrees. GM sets P0A9C (Type B, two trips) when sensor A deviates from the average of the others by more than 25 °C for 50 of 67 samples (19OBDG02); Two-Mode hybrids use more than 15 °C against each other sensor for 90 of 100 samples, other programs more than 20 °C. The check is suspended while circuit low/high codes are active, so P0A9C points to a sensor that reads wrongly but stays in range. GM's Volt bulletin 18-NA-342 lists it as sensor 1 performance and cures false sets with new module software. The pack then limits power to protect the cells.
- What you may notice
- Check engine light after two drive cycles
- Reduced hybrid assist or charging power
- Message such as battery too cold, plug in to warm (GM Volt)
- Likely causes
- LikelyThermistor drifted or poorly seated on its cell or module
- PossibleHigh-resistance connection in the sensor circuit shifting the reading
- PossibleBattery controller calibration causing false sets (GM Volt update)
- RareGenuine local temperature difference from a cooling or cell problem
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €60 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.