Rick's Free Auto Repair Advice

Car wont start with jump

My car won’t start with jump

If you’ve tried jump starting a dead battery and the car still won’t crank or cranks but won’t fire up, this post is for you. If your car won’t start with jump, start here

Most common causes when your car won’t start with jump

Mistake #1 The battery is severely discharged

The biggest mistake DIYers make when trying to jump-start a dead battery is thinking that the jump provides enough power to recharge the dead battery and still provide enough power to start the engine.

When you connect jumper cables to a severely discharged battery, the jumping power will first flow into the battery to recharge it before it will flow to the starter. So leave the jumper cables attached and DO NOT TRY STARTING THE DEAD vehicle for at least 10-minutes! Seriously, give it time to recharge the battery

Mistake #2 — Leaving power accessories on while trying to jump-start

Turn off the headlights, blower motor, heated seats, rear defogger in BOTH vehicles while you’re jumping the dead battery. A vehicle alternator can only output about 1/3 of its maximum capacity when idling, so there’s no way it can recharge the dead battery and still power all those electrical accessories at the same time.

If you’ve followed those instructions and the dead vehicle still won’t crank, try cleaning the battery posts and terminals. High resistance in the posts/terminals will prevent power from recharging the dead battery and the starter and probably caused the dead battery condition in the first place.

How to clean battery terminals

If you don’t know if the problem is a dead battery or bad alternator, read these articles:

Test your alternator

Find what’s draining your battery

Charge your battery

©, 2014 Rick Muscoplat

Posted on by Rick Muscoplat

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