Powertrain, generic · Hybrid propulsion

P0AC5 Hybrid/EV Battery Temperature Sensor B Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Battery temperature sensor B is one of several thermistors that measure cell or module temperature inside the high-voltage pack; GM's Volt bulletin calls it sensor 2 of nine. P0AC5 is the general circuit code for it, used for an electrical fault the controller does not classify as low, high or erratic. No manufacturer documents this exact code publicly; GM, for instance, reports P0AC6 to P0AC9 instead. CARB requires hybrid battery temperature inputs to be monitored for circuit faults. With one sensor missing the controller has a gap in its temperature picture and tends to limit charge and discharge power. The sensor usually sits on a module or sensing board inside the pack, so checks need high-voltage safety procedures.

Likely causes

Poor contact or damaged wire between sensor B and sensing board
Temperature sensor B failed
Fault in the battery controller input stage

Symptoms

  • Hybrid system or check engine warning
  • Reduced electric power and regeneration
  • Charging may be slower on plug-in models

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

hv battery temp sensor bwiring harnessbms

Related codes

P0AC6P0AC7P0AC8P0AC9P0A9BP0ACA

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