How to Jump-Start a Car Safely
Use the exact procedure in the vehicle owner’s manual. A common 12-volt sequence is positive on the disabled vehicle, positive and negative on the booster, then the final negative connection to the disabled vehicle’s designated ground away from its battery.
Timeline
- Before connecting: Check both manuals, battery condition, voltage, designated terminals and the surrounding area.
- Cable connection: Follow the vehicle-specific order and make the final ground connection away from the discharged battery.
- After starting: Disconnect in the manual’s reverse order, keep cables clear of moving parts and arrange diagnosis if the battery fails again.
Start with the disabled vehicle’s owner’s manual. Battery locations, remote jump terminals and safe grounding points vary, and some vehicles prohibit or modify ordinary jump-starting. NHTSA says an electric vehicle’s high-voltage traction battery cannot be jumped; only its 12-volt system may be jump-started in many models, using the manufacturer’s instructions. If either manual conflicts with a generic sequence, the manuals control. [1][2][3]
Do not proceed if a battery is cracked, leaking, visibly damaged, frozen or giving off an unusual odor, or if you cannot positively identify the correct terminals and system voltage. Keep flames, sparks and smoking materials away, wear eye protection, and do not lean over a battery. Use insulated, adequately sized cables. Keep the vehicles from touching, engage the parking brakes, select Park or Neutral as directed, switch off both vehicles and turn off electrical loads. [2][3][4]
For a typical negative-ground 12-volt system, the usual connection order is: connect red to the disabled vehicle’s positive terminal or remote positive post; connect the other red clamp to the booster battery’s positive terminal; connect black to the booster battery’s negative terminal; then connect the final black clamp to the disabled vehicle’s designated engine or chassis ground away from the battery and fuel system. Never improvise a grounding point. [2][3][4]
The final connection is made away from the discharged battery because connecting there can create a spark close to battery gas. Do not let clamps touch one another, bridge terminals with a tool, or route cables near fans, belts or other moving parts. Modern vehicles may have marked jump posts specifically to protect electronics and manage the battery system, so a visually accessible battery terminal is not automatically the right connection point. [2][3][4]
Start and run the booster vehicle only if its manual instructs you to do so, then attempt to start the disabled vehicle as directed. Do not keep cranking beyond the manual’s stated interval. Stop if cables become hot, smoke appears or the vehicle behaves abnormally. If the engine does not start after the permitted attempts, disconnect safely and call roadside assistance rather than repeatedly stressing the starter, battery or cables. [2][3][4]
After the disabled vehicle starts, disconnect in the exact order specified by its manual, commonly the reverse of connection: remove the clamp from the disabled vehicle’s ground, then booster negative, booster positive and disabled positive. Keep every loose clamp separated and away from moving parts. Close terminal covers and hoods only after all equipment is clear. The running vehicle may still stall if the battery or charging system has a fault. [2][3][4]
A jump start addresses a symptom, not its cause. A light left on, an aging battery, loose terminals, a parasitic drain or a charging-system problem can all produce a no-start condition. Have recurring failures diagnosed and follow the manual’s advice on how long to operate or charge the vehicle afterward. For a hybrid, EV, damaged battery or uncertain setup, use trained roadside service; do not touch orange high-voltage cables or components. [1][2][3]
Sources
- NHTSA — Electric and Hybrid Vehicle Battery and Jump-Starting Safety
- NHTSA Vehicle Owner Manual Record — Jump Starting Procedure
- NHTSA Vehicle Owner Manual Record — Jump Starting
- NHTSA Vehicle Owner Manual Record — Roadside Emergencies and Jumper Cables