Powertrain, generic · Hybrid propulsion

P0A9D Hybrid/EV Battery Temperature Sensor A Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Sensor signal wire shorted to ground or chafed inside the pack
Internally shorted thermistor on the sensing board
Moisture or coolant in the sensor connector
Battery controller software causing false sets (GM Volt)

Symptoms

  • Check engine or hybrid warning light
  • Strongly reduced electric power or no EV mode
  • Battery cooling running at high speed without reason

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

P0A9EP0A9CP0A9BP0A7EP0AC7

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