P0B31 code meaning
Hybrid/EV Battery D Voltage Low
Powertrain system Generic code P0Bxx codes Check engine light
What P0B31 means
P0B31 is stored when the voltage of hybrid/EV battery D stays below the expected range. High voltage of the same unit sets P0B32, fluctuation P0B30 and an unspecified deviation P0B2F. No manufacturer publishes a definition of P0B31; Bentley's P0B25 for battery A is the closest documented example, with the energy store replaced once the cell spread reaches 0.5 V. GM uses P0ABC for an undervoltage of the whole pack (below 24 V). CARB asks for monitoring of cells and voltage sensors in hybrid storage and for fault codes that single out the replaceable unit. Typical is a module in unit D that has aged faster or self-discharged during standstill. Discharge power and electric range drop, and the controller may stop electric driving.
P0B31 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 10 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0B31
- Hybrid/EV system or high-voltage battery warning on
- MIL on
- Battery power limited, less electric drive or assist
- Reduced electric range
Common causes of P0B31
- Most likelyAged cells with lost capacity in battery D
- PossibleDeep discharge or self-discharge after standstill
- Less likelyVoltage measurement fault in the controller or sense leads
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hv battery dBms
What each part of P0B31 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. |
| 31 | The exact fault in that area. |
What to do next
- Note P0B31 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 P0B31
What does P0B31 mean?
P0B31 means "Hybrid/EV Battery D Voltage Low". P0B31 is stored when the voltage of hybrid/EV battery D stays below the expected range. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B31?
Drive gently and only to a workshop. With P0B31 the car can go into limp mode (reduced power) to protect itself.
Will P0B31 fail an emissions test?
Yes, it can. P0B31 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 P0B31 to fix?
Difficulty: workshop only. A typical repair takes 1 to 10 hours of work. This is a job for a workshop.
Will P0B31 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.