P0B79: Hybrid/EV Battery Voltage Sense M Circuit Low

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.

High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
With the connector unplugged, check whether the signal wire is making contact with ground.
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

It can trigger limp mode.
It affects emissions.

What each character of P0B79 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
B: Subsystem depends on the code range
79: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0B79?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0B79?

The most common causes are: 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.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.