Powertrain, generic · Hybrid propulsion

P0AAC Hybrid/EV Battery Pack Air Temperature Sensor A Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Air-cooled hybrid batteries carry a thermistor in the cooling air path; GM calls sensor A the inlet air sensor. The battery controller uses it to run the fan and to judge cooling. P0AAC is the general circuit code, set for an electrical fault that is not classified as low, high or erratic. No manufacturer documents this exact code publicly; GM reports the siblings P0AAD to P0AAF instead, with Type B, two-trip logic. CARB requires hybrid component temperature sensors to be monitored like other input components. If the controller has no valid air temperature, it typically falls back to fixed fan control and may restrict battery power. Check connector and wiring at the air inlet duct first, then the sensor.

Likely causes

Loose, corroded or damaged sensor connector or wiring at the air duct
Failed air temperature thermistor
Battery controller input or reference voltage fault

Symptoms

  • Check engine or hybrid system warning light
  • Battery cooling fan runs constantly or at fixed speed
  • Reduced electric assist in hot conditions

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–2.5 h

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

Parts involved

hv battery pack air temp sensor awiring harnessbms

Related codes

P0AADP0AAEP0AAFP0AB0P0AB1

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com.