Powertrain, generic · Hybrid propulsion

P0A9C Hybrid/EV Battery Temperature Sensor A Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Thermistor drifted or poorly seated on its cell or module
High-resistance connection in the sensor circuit shifting the reading
Battery controller calibration causing false sets (GM Volt update)
Genuine local temperature difference from a cooling or cell problem

Symptoms

  • 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)

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€60–2,500
Time0.5–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hybrid battery temp sensor awiring harnessbms

Related codes

P0A9BP0A9DP0A9EP0A7EP0AC6

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.