P0A9C code meaning
Hybrid/EV Battery Temperature Sensor A Circuit Range/Performance
Powertrain system Generic code P0Axx codes Check engine light
What P0A9C means
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.
P0A9C at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0A9C
- 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)
Common causes of P0A9C
- Most 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)
- Less likelyGenuine local temperature difference from a cooling or cell problem
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hybrid battery temp sensor aWiring harnessBms
What each part of P0A9C means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| A | Area: hybrid propulsion. |
| 9C | The exact fault in that area. |
What to do next
- Note P0A9C and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0A9C
What does P0A9C mean?
P0A9C means "Hybrid/EV Battery Temperature Sensor A Circuit Range/Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0A9C?
Drive gently and only to a workshop. With P0A9C the car can go into limp mode (reduced power) to protect itself.
Will P0A9C fail an emissions test?
Yes, it can. P0A9C is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0A9C to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 5 hours of work. This is a job for a workshop.
Will P0A9C clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.