Powertrain, generic · Hybrid propulsion

P0AC9 Hybrid/EV Battery Temperature Sensor B Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P0AC9 catches a battery temperature sensor B signal that changes erratically. Pack temperatures move slowly because of the large thermal mass, so rapid swings point to a bad connection. GM documents the method in its 2016 and 2019 hybrid tables: the controller integrates the absolute change of the sensor value over a 10-sample window at 100 ms per sample; a window fails when the sum exceeds 10, and the code sets after 4 of 5 failed windows, Type B, two trips. The older two-mode and 2013 tables have no erratic code for this sensor. The fault is often intermittent and may clear by itself, so check connector locking and terminal tension at the sensing board.

Likely causes

Loose terminal or unlatched connector at the sensing board
Partly broken sensor wire inside the pack
Interference from high-voltage switching on the sensor line

Symptoms

  • Hybrid warning light that comes and goes
  • Sensor B value jumps in live data
  • Occasional power limitation

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–2,000
Time1–5 h

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

Parts involved

hv battery temp sensor bwiring harnessbms

Related codes

P0AC5P0AC6P0AC7P0AC8P0A9FP0ACE

References: gsi.ext.gm.com, gsi.ext.gm.com.