Powertrain, generic · Hybrid propulsion

P0A9E Hybrid/EV Battery Temperature Sensor A Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

With the NTC thermistor of sensor A on a pull-up circuit, an open sensor or wire drives the input voltage toward the reference, which the controller reads as an extremely cold cell. GM sets P0A9E (Type B, two trips) when the value falls below -69 °C in 8 of 10 samples (19OBDG02); Two-Mode hybrids flag readings below -45 °C, other programs below -40 °C for 1.4 s. GM's Volt bulletin 18-NA-342 lists it as sensor 1 circuit high voltage and pairs it with a battery too cold message at mild ambient temperatures. Unlike P0A9D the fault suggests an open circuit rather than a short. Because cold cells accept little current, the car restricts charging, regeneration and electric drive.

Likely causes

Open sensor wire or unplugged connector inside the pack
Open (failed) thermistor on the sensing board
Signal shorted to the reference voltage
Battery controller software causing false sets (GM Volt)

Symptoms

  • Check engine or hybrid warning light
  • Battery too cold message although it is not cold
  • Little or no electric drive and weak regeneration

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

P0A9DP0A9CP0A9BP0A9FP0AC8

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