Disassemble a vehicle in a fixed order: chock it on level ground, disconnect the battery negative terminal first, wait before touching airbag areas, relieve fuel and coolant pressure, support the body on stands, and only then release springs and open lines. The order matters because each step removes a stored energy that would otherwise injure you at the next one.
A vehicle is a collection of stored energies: electrical in the battery, chemical in the fuel, explosive in airbags and pretensioners, pressure in cooling, fuel and air-conditioning systems, and tension in springs. Most injuries come from releasing one of them by surprise.
Each Stored Energy Has A Sign You Can See And A Step That Removes It
| Stored energy | How to recognise it | Step that removes it |
|---|---|---|
| Battery, 12 V | Under the bonnet or in the boot, with two heavy cables | Remove the negative terminal first |
| Airbag, seat-belt pretensioner | Panels marked SRS or AIRBAG, tear seams in the steering wheel hub, dashboard and pillars | Battery off, wait, then follow the airbag steps |
| Fuel pressure | Fuel lines and injector rail on fuel-injected engines | Relieve pressure before opening any line |
| Cooling pressure | Radiator and its cap, hot hoses | Let the engine cool; never open a warm radiator cap |
| Springs | Coil springs on struts, leaf spring packs | Compress or clamp before release |
| Air-conditioning refrigerant | Metal pipes with service caps, compressor | Leave closed, or open slowly outdoors, protected |
| Vehicle weight | The whole car | Stands or cribbing, never a jack alone |
The method below puts these in the order that keeps you safe, and the linked pages give the detail.
What You Need
- Jack stands or cribbing, wheel chocks.
- Insulated or taped wrenches, gloves, eye protection, boots.
- Spring compressor, drain pans and sealable containers, rags, sand.
- A partner, and a first-aid kit.
Method: The Order Of Operations
Step 1: Position. Park on level ground in the open, chock the wheels and set the brake.
Step 2: Battery. Remove the negative terminal first, then the positive, and take the battery out if you intend to work near wiring. See Battery & Electrical Safety.
Step 3: Wait. The parent article advises waiting 10 minutes after disconnecting before working near airbag locations. See Mechanical Hazards.
Step 4: Fuel. Relieve fuel pressure before opening any fuel line, and have a container and sand ready. See Fire & Vapor Safety.
Step 5: Cooling. Let the engine cool before touching the radiator or hoses.
Step 6: Support. Put stands or cribbing under the frame before you go underneath.
Step 7: Release the springs and open the lines with the tools and methods the specific page describes.
Step 8: Drain fluids into labelled containers; see Fluids: Oil, Coolant, Brake Fluid.
Step 9: Cut and unbolt.
Common Mistakes
- Starting at the engine. Take the stored energies off first.
- Taking the positive terminal first. A tool touching the body then shorts it.
- Working under a car on a jack. The vehicle falls without warning.
- Cutting an airbag wire bundle “to see what is behind it.” It can trigger the unit.
- Rushing the last trip. Fatigue shortens the checks.
Safety
Every step in the order protects against the next
A battery can short through a wrench and weld it; airbags and pretensioners can fire during removal; fuel lines spray; hot coolant scalds; springs release their energy; a vehicle weighing 1,500-3,000 kg (parent article) is invariably fatal when it falls off a jack. If you are unsure whether something is safe to touch, leave it in place and work around it. Never work alone, and never skip a step because the previous one looked harmless.
What’s Next
- Learn next: Battery & Electrical Safety — the first hazard in the order
- Combine with: Mechanical Hazards — springs, airbags and pressurised systems