P0B40 code meaning
Hybrid/EV Battery Voltage Sense B Circuit
Powertrain system Generic code P0Bxx codes Check engine light
What P0B40 means
P0B40 is the circuit code of cell voltage sense channel B, the second cell or cell group the battery monitoring electronics measures; pack-level voltage uses P0ABA and P0B14 ff instead. GM applies the same open sense line test as on channel A: a 1.3 V jump between neighbouring cells, under 36 mV with balancing on, or splice voltage above 0.1 V (bus bar 0.5 V) for 0.6 s, Type A, one trip. Ford lists P0B40 among the open-line codes on the 2019-2020 Fusion PHEV, where the fix is a new traction battery, and on the 2023 Mustang Mach-E and e-Transit, where an intermittent flexible printed circuit cable in the battery controller is to blame. Expect no start or no charging.
P0B40 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 8 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0B40
- Wrench indicator or MIL, Stop Safely Now message possible
- No start condition
- Battery cannot be charged
Common causes of P0B40
- Most likelyOpen cell sense line, splice or bus bar connection inside the pack
- PossibleIntermittent flexible printed circuit cable in the battery controller (Ford Mach-E, e-Transit)
- PossibleInternal traction battery failure requiring replacement (Ford Fusion PHEV)
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 bWiring harnessBms
What each part of P0B40 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. |
| 40 | The exact fault in that area. |
What to do next
- Note P0B40 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 P0B40
What does P0B40 mean?
P0B40 means "Hybrid/EV Battery Voltage Sense B Circuit". P0B40 is the circuit code of cell voltage sense channel B, the second cell or cell group the battery monitoring electronics measures; pack-level voltage uses P0ABA and P0B14 ff instead. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B40?
Drive gently and only to a workshop. With P0B40 the car can go into limp mode (reduced power) to protect itself.
Will P0B40 fail an emissions test?
Yes, it can. P0B40 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 P0B40 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 8 hours of work. This is a job for a workshop.
Will P0B40 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.