What it means
The control module monitors voltage in hybrid/EV battery B and sets this code when the measured voltage falls below the expected range. The code identifies a low-voltage condition; it does not by itself establish whether the battery or its sensing circuit caused it.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Hybrid/EV battery B is a monitored high-voltage battery section or assembly whose voltage is measured by the battery control system. P0B29 sets when battery B's reported voltage falls below the allowed range; this can come from a depleted section or from a fault that makes its measured voltage appear low.
Common causes
Most likely first.
- Battery B voltage below expected range
- Voltage measurement circuit fault
- Loose or poor electrical connection
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
How to diagnose it
- Record freeze-frame data and compare battery B's live voltage with other sections, noting whether the low reading occurs under load, at rest, or during charging.
- Check for companion battery or charging codes that may help explain why battery B voltage is low.
- With the high-voltage system made safe using the manufacturer's procedure, inspect battery B connections and sensing wires for looseness, corrosion, or damage.
- Observe whether battery B voltage recovers during charging or drops disproportionately under load compared with other sections.
- Test the battery B measurement circuit and battery section to the manufacturer's specifications before selecting a repair.
Common fixes
- Secure or clean a loose or corroded battery B connection.
- Repair damaged battery B voltage-sensing wiring or terminals.
- Service or replace battery B if testing confirms that the section is below the expected voltage.
Can I keep driving?
Limit driving and avoid hard acceleration, as the vehicle may cut propulsion or charging when battery B voltage is low. If it enters limp mode or the warning is severe, stop safely and arrange service.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.