P0B79 code meaning
Hybrid/EV Battery Voltage Sense M Circuit Low
Powertrain system Generic code P0Bxx codes Check engine light
What P0B79 means
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.
P0B79 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 8 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0B79
- MIL and service hybrid or EV system message
- Electric drive or assist disabled
- Engine runs continuously on hybrids
Common causes of P0B79
- Most likelySense lead M shorted to ground or a lower cell potential
- PossibleFailed measuring input on the monitoring board
- Less likelyCell or NiMH block on channel M actually collapsed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hv battery voltage sense mWiring harnessBms
What each part of P0B79 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B | Area: hybrid propulsion. |
| 79 | The exact fault in that area. |
What to do next
- Note P0B79 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0B79
What does P0B79 mean?
P0B79 means "Hybrid/EV Battery Voltage Sense M Circuit Low". P0B79 means that the voltage reported for sense M is too low to be real. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B79?
Drive gently and only to a workshop. With P0B79 the car can go into limp mode (reduced power) to protect itself.
Will P0B79 fail an emissions test?
Yes, it can. P0B79 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0B79 to fix?
Difficulty: workshop only. A typical repair takes 1 to 8 hours of work. This is a job for a workshop.
Will P0B79 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.