do you remove jumper cables while car is running

[RemingtonLee]

No, you should never remove jumper cables while either car is running. Shut off both engines before disconnecting the cables. The primary risk is causing a significant voltage spike that can damage sensitive electronic components in one or both vehicles, such as the Engine Control Unit (ECU), infotainment systems, or sensors. Modern cars are packed with complex electronics that are highly vulnerable to power fluctuations.

The correct, safe sequence is crucial. After the disabled car starts, let both vehicles run for a few minutes to stabilize the electrical systems. Then, with both engines still running, carefully remove the cables in the reverse order of how you put them on. This means disconnecting the negative clamp from the previously dead car's ground first, then its negative clamp from the booster car, followed by the positive clamp from the booster car, and finally the positive clamp from the jumped car. This sequence minimizes the chance of creating a spark near the battery, which could ignite hydrogen gas emitted from the battery.

The risks of removing cables while the car is running are not always immediate, but the potential for expensive damage is very real. It’s a simple step that protects your vehicle’s expensive electronics.

Risk of Removing Cables While Running	Consequence	Correct Action
Voltage Spike	Damages ECU, alternator, infotainment system	Turn off both engines before disconnecting
Electrical Arc/Sparks	Can ignite battery hydrogen gas, causing explosion	Follow reverse connection order (negative off first)
Alternator Stress	Causes premature wear or failure on the booster car	Let both cars run to stabilize before shutdown
Erratic Computer Behavior	Triggers warning lights and sensor faults	Ensure solid connections and stable idle before disconnecting
Battery Management System Damage	Permanently affects charging in modern EVs/vehicles	Use a proper grounding point, not the dead battery's negative terminal

[LeMila]

Turn everything off first. I learned this the hard way years ago. I was in a hurry and pulled the cables off while my truck was running. It fried a voltage regulator, which meant a tow and a way bigger bill than I expected. Now, I always shut both cars down. It takes ten extra seconds and saves you from a major headache. Just let the jumped car run for a bit to charge, then turn the key off on both vehicles before you touch those clamps.

[OIvan]

It's all about preventing a power surge. Your car's alternator is working hard to recharge the dead battery. If you break the circuit suddenly by removing the cables, the voltage can spike. That spike travels through the electrical system and can easily fry computers that control the engine or transmission. The safest method is to turn off the booster car, then the jumped car, before you carefully remove the clamps in reverse order. This ensures a controlled shutdown of the charging system.

[DiLeah]

Think of it like unplugging a computer without shutting it down—you’re asking for trouble. Modern cars are basically computers on wheels. A sudden disconnect while the system is under load can scramble expensive modules. The official procedure from every mechanic I know is to let the car run for a few minutes, then shut it off before disconnecting. This allows the electrical system to settle. It’s a minor inconvenience that protects against a multi-thousand-dollar repair bill for new control units.

[PiperFitz]

Absolutely not. The key is to avoid sparks and power spikes. After the dead car starts, leave both running for about five minutes. Then, turn the ignition off on both cars. Now, disconnect the cables: start with the negative clamp on the jumped car's chassis, then the negative on the booster car, then the positive on the booster, and finally the positive on the jumped car. This reverse order keeps sparks away from the batteries, which is a critical safety step. It’s a simple habit that ensures everyone stays safe and their cars undamaged.