MajorCommonElectrical

BYD Seal: Car goes completely dead / can't be unlocked (12V and BMS software)

Car goes completely dead / can't be unlocked (12V and BMS software) is a common electrical fault on the BYD Seal on the 2023 onward cars, and we rate it major. Putting it right costs $250 to $700 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 6 documented faults on the BYD Seal.

Vehicle: BYD Seal
Years: 2023 onward
Fuel: ev
System: Electrical

This page covers the BYD Seal as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All BYD Seal faults6 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the 12V battery yet. We would rather show none than show a picture of a different part.

What goes wrong

2023-24 Seals are documented becoming completely unresponsive - unable to unlock or start despite the main Blade battery being well charged - typically after the car has sat for a few days or while plugged in at home. The fault traces to the 12V system and how the software tops it up while the car is idle, and BYD addresses it with a BMS/gateway software update through a dealer. There is no formal NZ recall, so an out-of-warranty 12V battery replacement is owner-paid. Combined with BYD's known parts and service delays in Australia and NZ, being stranded by this can mean a long wait for help.

What you would notice

Car totally dead, won't unlock or wake
Happens after sitting a few days or while home-charging
Needs a jump pack or dealer intervention to recover
12V battery warning messages

How to check it

Where to look. 12V auxiliary battery under the bonnet; BMS/gateway software

Ask the seller to leave the car locked and untouched overnight, then unlock and power it up yourself first thing.
Open the bonnet and check the 12V battery date and terminals.
Ask for service records showing the BMS/gateway software update has been applied, and whether the car has ever been 'bricked' and needed recovery.

Parts involved: 12V battery.

What it costs to put right

$250 to $700 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has the car ever gone completely dead and refused to unlock?”
“Has the BMS/gateway software update been done at a BYD dealer?”
“Has the 12V battery been replaced, and when?”

Now check the BYD Seal you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

Australian Car.Reviews - 'Recalls & faults: BYD Seal (2023-on)'
CarsGuide - 'BYD Seal Problems & Reliability Issues'
Geekzone NZ forum - '12 Volt Battery Failures in BYD EVs' (topic 303207)

BYD Seal buyer questions

Is car goes completely dead / can't be unlocked (12v and bms software) serious on a BYD Seal?

We rate it major and common on the BYD Seal. 2023-24 Seals are documented becoming completely unresponsive - unable to unlock or start despite the main Blade battery being well charged - typically after the car has sat for a few days or while plugged in at home. The fault traces to the 12V system and how the software tops it up while the car is idle, and BYD addresses it with a BMS/gateway software update through a dealer. There is no formal NZ recall, so an out-of-warranty 12V battery replacement is owner-paid. Combined with BYD's known parts and service delays in Australia and NZ, being stranded by this can mean a long wait for help.

How much does it cost to fix on a BYD Seal?

$250 to $700 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which BYD Seal years are affected?

Our research records this fault on the 2023 onward BYD Seal. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.

How do I check for it before I buy?

Ask the seller to leave the car locked and untouched overnight, then unlock and power it up yourself first thing. Open the bonnet and check the 12V battery date and terminals. Ask for service records showing the BMS/gateway software update has been applied, and whether the car has ever been 'bricked' and needed recovery. Look here: 12V auxiliary battery under the bonnet; BMS/gateway software