P0B78 code meaning
Hybrid/EV Battery Voltage Sense M Circuit Range/Performance
Powertrain system Generic code P0Bxx codes Check engine light
What P0B78 means
With P0B78 the controller doubts the reading of channel M rather than its wiring. GM's 2019 hybrid powertrain processor watches for a frozen value: whenever the average of all cells moves by more than 0.022 V, cell M must follow by at least 0.005 V in the same direction, and 35 failures in 40 samples at 100 ms set a Type A fault. The 2012 two-mode trucks map M to nickel-metal hydride block 13 and multiply blocks 13 and 14 by twenty; if that estimate misses the pack voltage by more than 70 V in 160 of 170 samples, the code is stored as Type B. The BAS Plus mild hybrid wants at least half the average movement, 20 of 40 samples, Type B. A plausible but wrong value is often a controller or measuring board issue.
P0B78 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0B78
- MIL on, often without noticeable driving change
- Reduced electric assist or regeneration
Common causes of P0B78
- Most likelyMeasuring channel M stuck at a fixed value
- PossibleBattery controller software needing an update
- Less likelyBlock 13 voltage drifting from the pack on two-mode NiMH packs
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 P0B78 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. |
| 78 | The exact fault in that area. |
What to do next
- Note P0B78 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 P0B78
What does P0B78 mean?
P0B78 means "Hybrid/EV Battery Voltage Sense M Circuit Range/Performance". With P0B78 the controller doubts the reading of channel M rather than its wiring. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B78?
Drive gently and only to a workshop. With P0B78 the car can go into limp mode (reduced power) to protect itself.
Will P0B78 fail an emissions test?
Yes, it can. P0B78 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 P0B78 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 6 hours of work. This is a job for a workshop.
Will P0B78 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.