P0A9DHybrid/EV Battery Temperature Sensor A Circuit Low
- 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
- Sensor A is an NTC thermistor fed through a pull-up resistor, so the voltage falls as the temperature rises; a short to ground looks like an absurdly hot cell. GM sets P0A9D (Type B, two trips) when the converted value exceeds 160 °C in 8 of 10 samples (19OBDG02); Two-Mode hybrids use above 95 °C while the other sensors read below 70 °C, other programs above 87.5 °C for 1.4 s. GM's Volt bulletin 18-NA-342 names it sensor 1 circuit low voltage. The low-voltage case is the counterpart of P0A9E (open circuit, reads very cold) and differs from P0A7E, which reports a real overtemperature. Because the controller must assume heat, it cuts charge and discharge power and may run cooling at full speed.
- What you may notice
- Check engine or hybrid warning light
- Strongly reduced electric power or no EV mode
- Battery cooling running at high speed without reason
- Likely causes
- LikelySensor signal wire shorted to ground or chafed inside the pack
- PossibleInternally shorted thermistor on the sensing board
- RareMoisture or coolant in the sensor connector
- RareBattery controller software causing false sets (GM Volt)
- 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.