P0B79Hybrid/EV Battery Voltage Sense M Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- MIL and service hybrid or EV system message
- Electric drive or assist disabled
- Engine runs continuously on hybrids
- Likely causes
- LikelySense lead M shorted to ground or a lower cell potential
- PossibleFailed measuring input on the monitoring board
- RareCell or NiMH block on channel M actually collapsed
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €6,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.