Why This Comes Before Every Other BYD Job
If a job touches the high-voltage side of a BYD — replacing the compressor, repairing a charge port, opening a cooling circuit, removing a battery pack shield — then step one is not a bolt. Step one is confirming the high-voltage system is dead. Get that wrong and every operation after it is a gamble.
BYD publishes the procedure in its BYD Emergency Response Guide, a document written for firefighters and rescue crews. The procedure itself applies just as well in a workshop. The problem is that it exists as a per-model PDF, and no consolidated English version circulates online. This page is that procedure, structured so a technician can follow it on a lift. Use it as the BYD high voltage shutdown reference before any work that touches orange cabling.
Two Official Disable Methods, and the Order Matters
BYD specifies two independent paths for a BYD high voltage disconnect. In a normal service situation you do both, in this order:
- Disconnect the low-voltage battery negative terminal. Press START/STOP, then keep the smart key at least 3 m (9.8 ft) away from the vehicle so it cannot be re-awakened. On models such as the Sealion 5 the 12V battery sits under the passenger seat — lift the access cover to expose the negative terminal and the ground harness, then disconnect it.
- Disconnect the high-voltage cable at the motor controller. Open the hood, wear insulating gloves, and follow the label instructions on the DC high-voltage connector to release it.
The order is not arbitrary. Killing the 12V side first removes the vehicle’s ability to re-energise contactors or wake a module while you are working near the pack. Cutting the high-voltage connector first leaves a live control system that can still act on what you are touching.
Deployed Airbags Are Themselves a Disable Trigger
This is the part most workshops do not know. When the restraint control module (RCM) fires an airbag or pretensioner, it simultaneously triggers a pyrotechnic fuse that deactivates the high-voltage system. BYD’s design intent is that an airbag deployment de-energises every high-voltage component and cable outside the battery pack itself.
Two timing numbers matter, and both are easy to get wrong:
- The high-voltage system is de-energised approximately 60 seconds after the deactivation event. Do not treat the car as safe the moment the airbags go off.
- The RCM carries an internal energy reserve and stays powered for roughly 10 seconds after the 12V supply is cut. Do not touch the RCM within 10 seconds.
So a collision-damaged BYD that arrives at your shop has probably already shut its own high voltage down. That does not make it safe, and it does not replace the manual procedure — it just explains why the car may not respond the way you expect when you probe it.
Shutdown Does Not Mean De-Energised
The single most important sentence in the whole guide: even though the high-voltage system has shut down due to airbag deployment, it must always be assumed that there may be high voltage present in the high-voltage cables and components. The cells inside the pack store energy and must not be compromised with rescue tools.
Practically, for anyone working on a BYD high voltage battery system:
- Orange = high voltage. Never cut, crush, or probe orange cabling.
- Never breach the pack when lifting from underneath. Do not compromise the floor pan or the battery enclosure with any tool.
- Do not open, cut, or disassemble any high-voltage component without the correct PPE.
Where the High-Voltage Hardware Actually Is
On the Sealion 5 the manufacturer documents six high-voltage assemblies: the front motor, two runs of high-voltage busbars, the high-voltage battery pack, the charge port, and the rear motor. The pack itself is floor-mounted, rated at 352 V / 268.8 V depending on configuration, and uses LFP chemistry with liquid cooling. The coolant is pink, which gives you a fast visual tell in the bay.
Coolant Leakage Is a Thermal Runaway Warning, Not a Leak
If the battery cooling circuit has been damaged, treat it as a safety event rather than a fluid loss. BYD states plainly that when coolant leakage occurs from the pack, the battery pack may become unstable and there is a risk of thermal runaway. The required action is to check pack temperature with a thermal imaging camera before doing anything else.
This is a different failure mode from a motor coolant weep. A motor loop leak is a repair. A pack coolant leak is an evacuation-and-monitor situation.
If the Vehicle Is on Fire — the Official Line
The guide is explicit that battery fires are fought with large volumes of water, applied directly to the battery, and that water supply must be established or requested early. Key points a workshop should know if a car starts smoking in the yard:
- Use a thermal imaging camera (TIC) to monitor pack temperature. Keep applying water until the pack temperature is at or below ambient.
- Do not open the pack to cool it. Do not submerge the vehicle to extinguish or cool a battery fire.
- BYD does not recommend foam on electric vehicles.
- Battery fires can take up to 24 hours to fully cool.
- Before the vehicle is released or moved, there must be no fire, smoke, audible popping or hissing, and no heating for at least 45 minutes.
- Because of re-ignition risk, a vehicle with a compromised pack should be stored in the open, at least 15 m (50 ft) from any other object.
The gases released are not ordinary combustion products — they can include hydrogen, carbon monoxide, hydrogen fluoride and metal-oxide particulates. Full PPE with SCBA is the responder standard, and downwind civilians need protecting.
Submerged Vehicles
A submerged BYD is handled like any other submerged vehicle — the body does not present a greater shock risk just because it is in water. The difference is fire risk: a water-damaged pack can ignite later. Raise the front of the vehicle to drain water out of the pack area, then carry out the normal shutdown procedure from Chapter 3 once it is out of the water.
What This Means for an Independent Workshop
Three rules fall out of the manufacturer’s own document:
- Never work on a BYD high-voltage system without completing the shutdown sequence and waiting out the de-energising window. The 60-second figure is a manufacturer number, not a rule of thumb.
- Assume every orange cable is live. Shutdown removes the drive, not the stored energy.
- Pack-level work is not independent-shop work. Mechanical work around a pack — lifting, shielding, mount torques — is within reach. Opening a pack is not, and BYD’s own language treats breaches as potentially fatal.
None of this is a substitute for the manufacturer’s guide or for the training that goes with high-voltage work. It is the manufacturer’s own procedure, in English, in one place, so you can start from the right document instead of a forum guess.
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Companion Pages: Putting These Documents to Work
The manuals above are the source. These pages are the extracted, workshop-ready versions of what is inside them.
- BYD battery fire and thermal runaway response — A flooded or collision-damaged car arrives — the 24-hour cooling figure, the 45-minute release window, the 15 m isolation distance, and the four methods BYD rules out.
- BYD Dolphin fuse box diagram — Chasing an electrical fault — all 53 under-hood and 31 dashboard positions, and the component each one protects.
- BYD coolant type and capacity — Booking a cooling job — the published specification and fill volume for all ten current models, and which ones run two circuits.
- BYD warning light meanings — A customer reports “a light came on” — which lamps mean stop now, which mean book it in, and the electric-only symbols.
- BYD Atto 3 service schedule — Taking a service booking — every interval, the four items with independent replacement cycles, and the severe-duty tightening.
Source
Compiled from the official BYD Sealion 5 Emergency Response Guide (English edition) — vehicle disable and safety regulations, stored energy and liquids, fire response, and submersion procedures. Model-specific hardware locations and pack ratings are quoted for the Sealion 5; the shutdown principle and timing apply across the current BYD range, but always confirm against the guide for the exact model on your lift.