Powertrain, generic · Hybrid propulsion

P0B79 Hybrid/EV Battery Voltage Sense M Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B79 means that the voltage reported for sense M is too low to be real. GM's lithium-ion battery controllers of 2016 and 2019 set it at 0.2 V or less, held for 1.4 s inside a 2 s window, Type A, and only while no open sense line fault is active, so a broken lead is reported by P0B77 first. On the 2012 two-mode hybrids M is block 13: the battery pack control module needs block 13 and block 14 both below 2 V in 15 of 20 samples, Type B. The BAS Plus mild hybrid uses 1.4 V, 7 of 10 samples, with the 12 V supply above 8.8 V. Typical sources are a sense lead shorted towards ground or a lower cell, a failed measuring input, or rarely a cell that has truly collapsed.

Likely causes

Sense lead M shorted to ground or a lower cell potential
Failed measuring input on the monitoring board
Cell or NiMH block on channel M actually collapsed

Symptoms

  • MIL and service hybrid or EV system message
  • Electric drive or assist disabled
  • Engine runs continuously on hybrids

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–6,000
Time1–8 h

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

Parts involved

hv battery voltage sense mwiring harnessbms

Related codes

P0B77P0B78P0B7AP0B7BP0B74P0B7E

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