Jump Start Procedure

Jumping a dead battery seems simple. Connect cables, start the car, done. But the order of connection matters. The location of the ground clamp matters. Getting it wrong can cause a battery explosion, destroy electronic modules, or injure you. Learn the right procedure and use it every single time.

Batteries produce hydrogen gas during charging and discharging. Hydrogen is explosive. When you connect or disconnect a cable from a battery terminal, the small spark at the connection point can ignite that gas. The last connection you make is the one most likely to spark. That is why the last connection must be made away from the battery — on the engine block or a designated ground point under the hood.

Step one — connect the positive (red) cable to the positive terminal of the dead battery. Step two — connect the other end of the positive cable to the positive terminal of the good battery. Step three — connect the negative (black) cable to the negative terminal of the good battery. Step four — connect the other end of the negative cable to a solid metal ground point on the engine block or frame of the dead vehicle — not the dead battery negative terminal. This keeps any spark far from the hydrogen gas concentrated around the dead battery. Start the vehicle with the good battery first, let it run for a few minutes to put some charge into the dead battery, then start the dead vehicle.

Remove cables in the exact reverse order. Engine block ground first, then good battery negative, then good battery positive, then dead battery positive. This ensures any spark during disconnection also happens away from the batteries.

Connecting positive to negative — reversed polarity — sends current backward through every electronic module on the vehicle simultaneously. Modern vehicles have dozens of computers. Reversed polarity can destroy the PCM, BCM, instrument cluster, infotainment system, and ABS module in the fraction of a second it takes to realize the mistake. Some vehicles have a main fusible link that blows to protect the system. Many do not. The repair bill for a reversed polarity jump start can exceed the value of the vehicle. Always verify terminal markings before connecting cables.