Powertrain, generic · Hybrid propulsion

P0A9B Hybrid/EV Battery Temperature Sensor A Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Temperature sensor A is one of the thermistors the battery controller uses to track cell or module temperature for cooling, charge limits and power limits. P0A9B is the general circuit code for this sensor: the controller finds an electrical fault it does not classify further as low, high or erratic. No manufacturer documents this exact code publicly; GM, for example, reports the sibling codes P0A9C to P0A9F instead. In those tables a failed sensor input is excluded from protection logic, and GM's Volt bulletin notes several sensors per pack. Expect a hybrid warning and reduced charge and assist power while the controller works with fewer valid temperatures. Check the sensor harness at the module sensing board before condemning the pack.

Likely causes

Open, corroded or loose sensor wiring or connector inside the pack
Failed thermistor on the module or cell sensing board
Battery controller input or software fault

Symptoms

  • Hybrid or EV system warning and check engine light
  • Reduced electric assist, regeneration or charging power
  • Battery cooling fan or pump runs more than usual

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–2,500
Time1–5 h

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

Parts involved

hybrid battery temp sensor awiring harnessbms

Related codes

P0A9CP0A9DP0A9EP0A9FP0AC5

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.