C12F909
Brake hydraulic circuit blocked
The intelligent power brake system has detected that brake fluid is not moving through the hydraulic circuit the way it expects. BYD's diagnostic documents trace this to the pressure the brake controller measures, to air or contamination in the fluid, or to a physical restriction in the lines.
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Severity varies by vehicle — Critical (8): BYD Sealion 07 2024, BYD Song L DM-i 2025, Denza D9 EV 2023, Denza D9 EV 2024, Denza N7 2025, Denza N9, Destroyer 05, Qin Plus; Warning (23): BYD D1 2023, BYD Dolphin 2021, BYD Han DM 2023, BYD Han EV 2023, BYD Overseas ATTO3 2025, BYD Overseas DOLPHIN 2025, BYD Overseas SEAL 2025, BYD Qin L 2024-2025, BYD Seagull 2023, BYD Seagull 2025, BYD Seal 2023, BYD Seal 2025, BYD Seal DM-i 2024, BYD Song L EV 2024, BYD Song PLUS 2021, BYD Song Pro DM-i 2022-2023, BYD Tang NEV 2021, BYD Tang NEV 2022, BYD Tang NEV 2023, BYD Tang NEV 2023 EV, BYD Yuan PLUS 2023, Denza N7 2023, Denza N7 2024.
What are the symptoms of C12F909?
- Part of the intelligent power brake system stops working
What causes C12F909?
Ordered by how many BYD-group vehicles list each cause for this code — not by how likely it is on your car.
- Pressure sensor inside the intelligent power brake controller — listed on 51 vehicles
- Air in the brake lines — listed on 39 vehicles
- Brake fluid degraded or contaminated — listed on 22 vehicles
- Blocked brake line — listed on 22 vehicles
Where do I start with C12F909?
Check the electro-hydraulic brake DTCs.
The full procedure for your vehicle
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Worth knowing
- BYD's high-voltage procedure calls for disconnecting the 12 V supply and waiting at least 5 minutes after shutdown before work begins.
Which vehicles does C12F909 affect?
- BYD D1 2023
- BYD Dolphin 2021
- BYD Han DM 2023
- BYD Han EV 2022
- BYD Han EV 2023
- BYD Han L DM 2025
- BYD Overseas ATTO3 2025
- BYD Overseas DOLPHIN 2025
- BYD Overseas M6(RHD) eMAX 7 2025
- BYD Overseas SEAL 2025
- BYD Overseas SEALION 07 2025
- BYD Overseas Song Plus 2024
- BYD Qin L 2024-2025
- BYD Seagull 2023
- BYD Seagull 2025
- BYD Seal 05 DM-i 2025
- BYD Seal 06 2025
- BYD Seal 2023
- BYD Seal 2025
- BYD Seal DM-i 2024
- BYD Sealion 07 2024
- BYD Sealion 07 2025
- BYD Song L 2024 4668
- BYD Song L DM-i 2025
- BYD Song L EV 2024
- BYD Song PLUS 2021
- BYD Song PLUS 2025
- BYD Song Pro DM-i 2022-2023
- BYD Tang L 2025
- BYD Tang NEV 2021
- BYD Tang NEV 2022
- BYD Tang NEV 2023
- BYD Tang NEV 2023 EV
- BYD Xia 2025-2026
- BYD Yuan PLUS 2023
- BYD Yuan UP 2024
- Denza D9 DM 2022
- Denza D9 DM 2025
- Denza D9 DM-i 2024
- Denza D9 DM-i 4-Seat 2023-2024
- Denza D9 EV 2023
- Denza D9 EV 2024
- Denza D9 EV 2025
- Denza D9 EV RHD 2025
- Denza N7 2023
- Denza N7 2024
- Denza N7 2025
- Denza N8 2023
- Denza N9
- Denza Z9 2025
- Destroyer 05
- Fangchengbao Bao 5 2023
- Fangchengbao Bao 5 2025
- Fangchengbao Bao 8 2025
- Fangchengbao Titanium 3 2025
- Qin Plus
- Yangwang U7 2025
- Yangwang U8 2023
- Yangwang U8 2024
- Yangwang U9 2025
Background reading
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