Is it safe to drive with this code?

Driving with P0B21 active may be possible in the short term if the vehicle remains in a limited-power mode, but the hybrid system's ability to function safely is compromised and continued use could lead to further damage or a breakdown—see our disclaimer and arrange inspection promptly.

The code itself isn't directly checked, but if the malfunction indicator lamp (engine warning light) is illuminated at the time of the MOT test, the vehicle may not pass—see our disclaimer for full MOT guidance.

Roughly how much does it cost to fix?

Costs vary widely depending on the root cause: a connector clean or wiring repair might fall in the low three-figure band, a voltage sensor replacement in the mid three-figure range, whilst reconditioning or replacing sections of the high-voltage battery pack can reach high three-figure to four-figure sums, particularly at main dealers—independent hybrid specialists often charge less for labour.

Can a normal garage diagnose this code?

Many independent workshops lack the specialised diagnostic equipment and high-voltage certification needed for hybrid systems—look for a garage with hybrid or electric vehicle training and the proper insulated tools to work safely on high-voltage components.

Professional mechanic working in workshop

← All fault codes | Electrical & Sensors

P0B21

Powertrain

Hybrid Battery Pack Voltage Sense "D" Circuit High

The hybrid system's voltage monitoring circuit for battery cell group 'D' is reporting a reading that's higher than the control module expects, which may indicate a sensor fault or wiring issue in that section of the high-voltage battery pack.

garage.co.uk

Need a garage?

Compare quotes from verified UK garages near you.

→

car.co.uk

Sell your car

We specialise in problem cars: warning lights, faults, high mileage. Fair instant offer.

→

trader.co.uk

List your car

Free private listing. Reach thousands of UK buyers, no fees.

→

ⓘ Information only. This page provides general educational information about fault code P0B21. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.

Recommended next steps

Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.

What does P0B21 mean?

P0B21 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Hybrid Battery Pack Voltage Sense "D" Circuit High.

This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.

About Electrical & Sensors codes

Codes in the Electrical & Sensors category.

P0B21 is one of 4,010 codes in this category. Browse all Electrical & Sensors codes →

What we know about P0B21 specifically

We record the SAE J2012 standardised definition and the system this code belongs to, but we have not yet published detailed driver-reported symptoms, common causes, or step-by-step diagnostic guidance for P0B21.

Rather than invent that information by generating generic content from a template, we leave it out. For specific guidance, the most reliable sources are:

•your vehicle's own service manual or manufacturer-specific technical bulletins
•a qualified mechanic with a manufacturer-level diagnostic tool
•a marque specialist familiar with your make and model

Codes nearby

Codes adjacent to P0B21 in the P-code series. Many fault codes appear together with their neighbours because they relate to the same circuit or component.

P0B1E Hybrid Battery Pack Voltage Sense "D" Circuit

P0B1F Hybrid Battery Pack Voltage Sense "D" Circuit Range/Performance

P0B20 Hybrid Battery Pack Voltage Sense "D" Circuit Low

P0B22 Hybrid Battery Pack Voltage Sense "D" Circuit Intermittent/Erratic

P0B23 Hybrid Battery "A" Voltage

P0B24 Hybrid Battery "A" Voltage Unstable

Other Electrical & Sensors codes

Other fault codes in the same system as P0B21. The ones with detailed guides have plain-English explanations, symptoms, causes, and diagnostic steps.

B1257

Air Temperature External Sensor Circuit Short To Ground Detailed guide

B1363

DBPT Circuit Short To Ground Detailed guide

B2100

Ignition Run/Start Input Circuit Performance Detailed guide

C2000

Steering Angle Sensor Not Calibrated Detailed guide

P0030

HO2S Heater Control Circuit (Bank 1 Sensor 1) Detailed guide

P0031

Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1) Detailed guide

Spotted an issue or have something to add? Mechanics, technicians, and drivers who have first-hand experience with P0B21 can submit a correction or expansion. We review every submission before publishing, mechanic submissions are prioritised.

Information only, not professional advice

The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →

✎

Help us improve the P0B21 page

Spotted an error, missing detail, or have first-hand experience to add? Tell us, we review every submission.