P0B51 code meaning
Hybrid/EV Battery Voltage Sense E Circuit Low
Powertrain system Generic code P0Bxx codes Check engine light
What P0B51 means
P0B51 tells that cell sense channel E reads near zero. GM's battery energy control module only runs this check under clear conditions: the module is in run, crank or accessory mode, the second protection self-test is not running, and no slave communication, open sense line, balancing or internal performance fault is active. Then a reading of 0.2 V or less for 1.4 s in a 2 s window sets the code, Type A, one trip. The order matters for diagnosis: an open sense line or a lost slave board would be reported first by their own codes. On the 2012 two-mode hybrids channel E is block 5, set when blocks 5 and 6 both drop below 2 V, Type B. Electric operation is then restricted.
P0B51 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.3 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0B51
- MIL and hybrid system warning
- Electric-only driving unavailable
Common causes of P0B51
- Most likelyChannel E sense line shorted to its neighbour
- PossibleFaulty input on the cell monitoring slave board
- Less likelyPin backed out of the monitoring harness connector
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 eWiring harnessBms
What each part of P0B51 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. |
| 51 | The exact fault in that area. |
What to do next
- Note P0B51 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 P0B51
What does P0B51 mean?
P0B51 means "Hybrid/EV Battery Voltage Sense E Circuit Low". P0B51 tells that cell sense channel E reads near zero. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B51?
Drive gently and only to a workshop. With P0B51 the car can go into limp mode (reduced power) to protect itself.
Will P0B51 fail an emissions test?
Yes, it can. P0B51 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 P0B51 to fix?
Difficulty: workshop only. A typical repair takes 0.3 to 6 hours of work. This is a job for a workshop.
Will P0B51 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.