Powertrain, generic · Hybrid propulsion

P0B29 Hybrid/EV Battery B Voltage Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B29 sets when the voltage of hybrid/EV battery B stays below the range the controller expects for the present state of charge and load. It is the low counterpart to P0B2A; fluctuating readings belong to P0B28 and the general fault to P0B27. No manufacturer publishes a definition of P0B29; Jeep 4xe bulletins confirm the use of a separately monitored battery B only through P0B28. GM handles the analogous whole-pack undervoltage with P0ABC (pack voltage below 24 V). CARB requires battery voltage sensors and cells to be monitored and the fault to be narrowed to the smallest replaceable unit. Weak or deeply discharged cells in that unit are the usual reason, so the controller cuts discharge power and may block driving in EV mode.

Likely causes

Aged cells with lost capacity in battery B
Deep discharge or self-discharge after standstill
Voltage measurement fault in the controller or sense leads

Symptoms

  • Hybrid/EV system or high-voltage battery warning on
  • MIL on
  • Battery power limited, less electric drive or assist
  • Electric-only driving unavailable

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–4,000
Time1–10 h

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

Parts involved

hv battery bbms

Related codes

P0B27P0B28P0B2AP0B25P0ABC

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