P0B29 on Audi: How to Diagnose & Fix
Hybrid Battery "B" Voltage Low
1 Audi model · 1 documented issue
P0B29 on Audi by model: symptoms, diagnosis and fix
Audi TSB 2067906/5 explains that the 48V battery can enter low-state-of-charge protection and open its internal relays. P0A7D00 can accompany this condition. When measured 48V state of charge is 5%-15%, Audi directs a controlled recharge through the 12V electrical system and says the 48V battery must not be replaced for that condition. P0B2900 alone is also not a reason to replace the battery. This is a guided service procedure, not proof of battery degradation.
Common Symptoms
- 48V battery state of charge at 5%-15%
- 48V low-state-of-charge protection active
How to Fix
Have an Audi-trained technician measure both battery states of charge and follow the current guided procedure. For a 48V battery at 5%-15%, TSB 2067906/5 requires an approved high-capacity 12V charger and the ODIS charging-contactor test plan; it is not a consumer battery-maintainer procedure. Audi permits replacement only when the 48V state of charge is below 5% or guided fault finding directs replacement. Do not buy a 48V battery, 12V battery, charger, tape, wire loom or connector kit from this diagnostic card.
Sources for this issue (1)
P0B29 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0B29 mean on a Audi?
P0B29 stands for "Hybrid Battery "B" Voltage Low." The battery energy control module monitors every cell block in the high-voltage or 48V battery pack to confirm each is contributing equally. P0B29 sets when the voltage measured across the block designated "B" falls below the calibrated threshold, or falls too far below the other blocks. In practice it means one section of the pack is weak, degraded, or not being sensed correctly - it is a cell-group-level complaint, not a whole-pack complaint. On Audi it is documented across 1 model: A6 allroad.
What are the most common causes of P0B29?
The most common causes of P0B29 are: Degraded or failing cell block within the battery pack, Poor connection at a cell-group busbar or voltage-sense connector, Faulty voltage-sense wiring harness inside the pack, Failed battery energy control module / cell supervision circuit, Battery pack imbalance from long storage or repeated deep discharge, On 48V mild-hybrid systems: failing 48V lithium battery or its DC/DC converter. The specific cause varies by vehicle.
How much does it cost to fix P0B29 on a Audi?
Repair costs vary widely with the root cause and Audi model; each issue on this page carries its own estimate where one is published.
Looking for P0B29 on a different make?
View P0B29 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.