can you jump start car with engine still on

[AliyahLynn]

No, you should never attempt to jump-start a car with the engine still running. This practice is highly dangerous and can cause significant damage to the electrical systems of both vehicles. When an engine is on, the alternator is actively charging the battery, creating a higher and unstable voltage. Connecting jumper cables at this point can lead to voltage spikes that may fry sensitive components like the ECU (Engine Control Unit), which manages engine functions, or damage the alternator itself. Additionally, it increases the risk of electrical shorts or sparks near the battery, which could ignite hydrogen gas emitted by the battery, posing a fire hazard.

The correct and safe procedure for jump-starting a car requires both engines to be completely off before any connections are made. This ensures that the electrical systems are stable and minimizes risks. Here's a brief overview of the proper steps:

1. Park the working car close to the dead car, but do not let them touch. Turn off both engines and engage the parking brakes.
2. Connect the red positive (+) clamp to the dead battery's positive terminal, then the other red clamp to the working battery's positive terminal.
3. Connect the black negative (-) clamp to the working battery's negative terminal, and the other black clamp to an unpainted metal surface on the dead car's engine block—not the negative terminal—to avoid sparks.
4. Start the working car's engine and let it run for a few minutes to transfer charge.
5. Attempt to start the dead car. If it starts, disconnect the cables in reverse order.

Modern vehicles with advanced electronics are particularly vulnerable to voltage irregularities. According to automotive best practices from sources like the AAA (American Automobile Association), jump-starting with engines off is standard to prevent costly repairs. If you're unsure, consulting a professional mechanic or using a portable jump-starter is a safer alternative.

[StPhoebe]

I tried jump-starting my buddy's car once while my engine was running, and it caused a flicker in my dashboard lights. Scared me straight! Now I always turn both cars off first. It's just not worth the risk of zapping something important, like the radio or computer. Takes an extra minute, but saves headaches later. Stick to the safe way—engines off, cables on, then fire it up.

[Grace]

Having tinkered with cars for years, I can say jump-starting with an engine on is a surefire way to invite trouble. The alternator is pumping out around 14 volts when running, and connecting to a dead battery can create a surge. This might overwhelm modules like the PCM (Powertrain Control Module), leading to expensive fixes. Always shut everything down, hook up the cables properly, and you'll avoid frying your vehicle's brains. It's basic electrical safety that every DIYer should follow.