Powertrain, generic · Hybrid propulsion

P0B4A Hybrid/EV Battery Voltage Sense D Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B4A is the open-circuit code of cell sense channel D, the fourth measuring channel of the battery monitoring electronics. GM checks it in the battery energy control module with the same open sense line logic as the other channels: a gap of 1.3 V or more between adjacent cells, under 36 mV on a cell being balanced, or splice voltages above 0.1 V or 0.5 V at a bus bar, for 0.6 s, Type A. For diagnosis, the pattern matters: if P0B4A stands alone, inspect the channel D tap and its connector; if Ford's whole open-line group from P0B3B upwards is set, as on the 2019-2020 Fusion PHEV or the 2023 Mach-E and E-Transit, a common cause such as the BECM flex cable or the battery itself is more likely.

Likely causes

Open channel D sense tap or connector (code set alone)
Faulty BECM flexible printed circuit affecting several channels (Ford Mach-E, E-Transit)
Internal traction battery fault (Ford Fusion PHEV)

Symptoms

  • No start or vehicle will not go into ready mode
  • Charging not possible
  • Several sense channel codes stored together

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–8,000
Time0.5–8 h

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

Parts involved

hv battery voltage sense dwiring harnessbms

Related codes

P0B4BP0B4CP0B4DP0B4EP0B45P0B4F

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