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.
High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.
Symptoms
- Wrench indicator or MIL, Stop Safely Now message possible
- No start condition
- Battery cannot be charged
Most likely causes
- Open cell sense line, splice or bus bar connection inside the pack
- Intermittent flexible printed circuit cable in the battery controller (Ford Mach-E, e-Transit)
- Internal traction battery failure requiring replacement (Ford Fusion PHEV)
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- It can trigger limp mode.
- It affects emissions.
What each character of P0B40 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- B: Subsystem depends on the code range
- 40: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0B40?
If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.
What causes code P0B40?
The most common causes are: open cell sense line, splice or bus bar connection inside the pack; intermittent flexible printed circuit cable in the battery controller (Ford Mach-E, e-Transit); internal traction battery failure requiring replacement (Ford Fusion PHEV).
Related codes
- P0B41Hybrid/EV Battery Voltage Sense B Circuit Range/Performance
- P0B42Hybrid/EV Battery Voltage Sense B Circuit Low
- P0B43Hybrid/EV Battery Voltage Sense B Circuit High
- P0B44Hybrid/EV Battery Voltage Sense B Circuit Intermittent/Erratic
- P0B3BHybrid/EV Battery Voltage Sense A Circuit
- P0B45Hybrid/EV Battery Voltage Sense C Circuit
Sources
- gsi.ext.gm.com: 19OBDG01 Hybrid Diagnostics
- static.nhtsa.gov: MC 10232489 0001
- static.nhtsa.gov: MC 11005840 0001
- law.cornell.edu: 13 CCR 1968.2
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.