What are the consequences of disconnecting the positive terminal of a car battery?

[MacHeidi]

The consequence of disconnecting the positive terminal of a car battery is that the battery will stop supplying power, some functions of the car may fail, and factory settings might be restored. Battery discharge: If the battery is discharged, the car will be difficult to start, and a charger can be used to recharge it. During long-term parking of the car, it is necessary to start the vehicle regularly, preferably once a week, allowing the car to idle for a period of time so that the internal alternator can charge the battery. Driving techniques: Due to driving techniques, some car owners may stall the car frequently, leading to repeated starts. The ignition time should not exceed 3 seconds. If the engine fails to start once, avoid repeated ignition attempts. Instead, wait for a 15-second interval before trying again. Otherwise, frequent supply of high current from the battery to the starter will cause its own wear and tear.

[SanHector]

I've experienced disconnecting the car battery's positive terminal twice. The first time was when I wanted to clean the engine bay, and casually removed it, resulting in a complete power loss. The dashboard clock reset to zero, the trip computer's fuel consumption data was all gone, and the most annoying part was having to reset over thirty radio stations stored in the system. Another time, a mechanic said it was necessary to disconnect the power for repairs, but after reconnecting, the one-touch window up/down function stopped working, and it took twenty minutes of fiddling with the manual to restore it. Important reminder: Never try this while driving! A friend of mine suddenly lost power on the highway, causing the steering wheel to lock up and nearly resulting in an accident. Disconnecting the battery also resets the ECU, and some cars require professional equipment to rematch the anti-theft system. It's recommended to have a professional handle such operations.

[VonElliott]

I usually enjoy studying car electrical systems, and the core issue with disconnecting the positive battery terminal is the chain reaction of power loss. All components that rely on electricity will stop functioning: for example, the electronic power steering will immediately become heavy, and the brake assist will disappear, making the pedal as hard as a rock. Reconnecting after a power cut can also leave hidden dangers: the infotainment system often resets to factory settings, requiring you to re-enter navigation destinations; some cars' auto start-stop function may also report errors. More seriously, sudden power loss can damage the generator voltage regulator, and replacing it can cost several hundred dollars. That's why professional repairs use a backup power supply connected to the fuse box to prevent data loss—ordinary car owners shouldn't attempt this themselves.

[LaSienna]

Last week, my car lock malfunctioned, and the mechanic suggested first cutting off the power to restart the circuit system. At the time, the positive terminal was disconnected and then reconnected, causing the entire vehicle to reset: five error codes popped up on the dashboard, and the air conditioning default temperature was set to the highest. The most troublesome issue was the failure of the reversing camera on the central control screen—it wouldn’t display even after shifting gears again. It took half an hour to reset everything. The mechanic said modern car circuits are like networks; a sudden power cut is like unplugging a network cable, causing modules to send out random error signals. Particularly, the reversing radar and tire pressure monitoring systems are prone to false alarms. So after a power cut, it’s usually necessary to visit the shop to clear the error codes with a computer rather than waiting for them to reset on their own.