P0B29: Hybrid/EV Battery B Voltage Low

P0B29 sets when the voltage of hybrid/EV battery B stays below the range the controller expects for the present state of charge and load. It is the low counterpart to P0B2A; fluctuating readings belong to P0B28 and the general fault to P0B27. No manufacturer publishes a definition of P0B29; Jeep 4xe bulletins confirm the use of a separately monitored battery B only through P0B28. GM handles the analogous whole-pack undervoltage with P0ABC (pack voltage below 24 V). CARB requires battery voltage sensors and cells to be monitored and the fault to be narrowed to the smallest replaceable unit. Weak or deeply discharged cells in that unit are the usual reason, so the controller cuts discharge power and may block driving in EV mode.

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

Hybrid/EV system or high-voltage battery warning on
MIL on
Battery power limited, less electric drive or assist
Electric-only driving unavailable

Most likely causes

Aged cells with lost capacity in battery B
Deep discharge or self-discharge after standstill
Voltage measurement fault in the controller or sense leads

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
With the connector unplugged, check whether the signal wire is making contact with ground.
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

It can trigger limp mode.
It affects emissions.

What each character of P0B29 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
B: Subsystem depends on the code range
29: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0B29?

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 P0B29?

The most common causes are: aged cells with lost capacity in battery B; deep discharge or self-discharge after standstill; voltage measurement fault in the controller or sense leads.

Related codes

Sources

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.