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DTC codes / P0Bxx · Hybrid propulsion / P0B29

P0B29Hybrid/EV Battery B Voltage Low

P0B29 indicates that the hybrid or electric vehicle battery control module has detected an abnormally low voltage condition in battery module B, which is one specific section of the high-voltage pack. The computer compares this module's voltage against expected values and flags the code when the reading falls below the calibrated threshold for a set period.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the hybrid system warning light or service vehicle soon message
  • Reduced electric-only range or the engine starting more frequently than usual
  • A noticeable drop in available power or sluggish acceleration under load
  • The vehicle may enter a reduced-power limp mode to protect the battery
  • Often no symptoms besides the warning light, especially in early stages
  • Inconsistent charging behavior or the battery gauge dropping faster than normal

Common causes, most likely first

  1. A weak or failing battery module B, often due to aged cells or internal resistance
  2. Poor electrical connection at the module B voltage sensing harness or connector
  3. Faulty voltage sensing wire or corroded terminal between the module and the battery control module
  4. An imbalance in state of charge across modules caused by a malfunctioning cell or module
  5. A software or calibration issue in the battery control module that misreports voltage
  6. Extreme ambient temperatures affecting temporary voltage readings, though usually not the root cause
  7. A failing battery control module itself, though this is less common than module or wiring faults

How to diagnose and fix it

  1. Use a scan tool to record freeze-frame data and verify the code is current, then check for related codes in the battery control module
  2. Inspect the module B voltage sensing harness and connector for corrosion, looseness, or damage, and repair as needed
  3. Measure the actual voltage of module B with a high-voltage-safe meter and compare it to the scan tool reading to confirm the fault
  4. Perform a battery pack state-of-health test and module balance check according to the manufacturer's service information
  5. If module B is consistently low, replace the faulty module or cell group following the manufacturer's high-voltage safety procedures
  6. After repair, clear codes and perform a battery pack relearn or calibration drive cycle as required
  7. If wiring and module voltage are normal, reprogram or replace the battery control module per service guidelines

What a low module B voltage really means

  • A low voltage reading on one module often points to a single weak cell group rather than the entire pack, so replacing the whole battery is usually unnecessary.
  • The code can be set by a loose or corroded voltage sense wire even when the module itself is perfectly healthy, so always check the harness before condemning the battery.
  • Temperature extremes can cause temporary voltage dips that trigger the code without a permanent fault, so verify the code returns after a full drive cycle before major repairs.
  • Some vehicles set P0B29 alongside imbalance codes or isolation fault codes, which can distract from the real issue if you only focus on the low voltage.
  • A battery control module software update may correct false low-voltage reporting on certain platforms, so check for technical service bulletins before replacing hardware.

Can I keep driving with P0B29?

You can usually drive the vehicle short distances to a service center, but avoid heavy acceleration, sustained high speeds, and deep discharging the battery. If the vehicle enters limp mode or multiple warning lights appear, stop driving and have it towed to prevent further battery damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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