Many car owners use OBD2 scanners for diagnostics, performance monitoring, or accessing various smart features in their vehicles. A common question arises: can I leave my OBD2 scanner plugged in all the time, or should I unplug it after each use? As an auto repair expert at obd-de.com, I’m here to provide a comprehensive answer.
The short answer is generally no, you should not leave your OBD2 scanner plugged in indefinitely. While it might seem convenient, leaving your OBD2 device connected can lead to potential battery drain. Let’s delve deeper into why this is the case and what you need to know.
The Persistent Power Draw of OBD2 Ports
The OBD2 port in your vehicle is designed to be a constant power source. As highlighted by @All2kool on E46Fanatics, according to international standards, pin 16 of the OBD2 port is always live. This means that anything you plug into this port, including your OBD2 scanner, will continuously draw power, even when your car is turned off.
While the current draw of most OBD2 devices is relatively small, often around 10mA in sleep mode, it’s not negligible. Think of it as a tiny parasitic drain on your car battery. In isolation, 10mA might seem insignificant. However, over days and weeks, especially if you don’t drive your car frequently, this constant drain can add up.
Consider this scenario: a typical car battery might have a self-discharge rate, and the car itself has some systems that draw power even when off (like the car alarm or ECU memory). Let’s say the car’s normal sleep consumption is 30mA. Adding another 10mA from a permanently plugged-in OBD2 scanner increases the total drain to 40mA. This 33% increase in parasitic draw can noticeably reduce your battery life over time.
For daily drivers, this small drain might not be immediately apparent. The alternator recharges the battery every time you drive, offsetting the minor drain. However, if you only use your car once or twice a week, or even less frequently, leaving your OBD2 scanner plugged in can contribute to a noticeably weaker battery and potentially lead to a flat battery, especially in colder climates where battery performance is already reduced.
Why Your OBD2 Device Might Appear Off
You might observe that your OBD2 scanner or app seems to be inactive when the ignition is off, leading you to believe it’s not drawing power. There are a couple of reasons for this perceived inactivity:
Firstly, some car manufacturers, like BMW in older models, implemented a switched power supply on pin 15 of the OBD2 port, in addition to the standard ISO 9141-2. This pin is only powered when the ignition is on and is often used for manufacturer-specific diagnostic tools like INPA to detect ignition status. However, this is not a universal standard, and most generic OBD2 devices will still draw power from the always-live pin 16.
Secondly, and more commonly, many OBD2 readers and apps employ battery voltage sensing to determine the car’s on/off state. They monitor the voltage level; when it drops below a certain threshold, typically around 13.2V, they assume the alternator is not running and the car is off. Consequently, they enter a sleep mode to minimize their own power consumption. However, as demonstrated by tests, even in “sleep mode,” these devices often still draw a small current (like the 10mA mentioned earlier) to remain connected and monitor the battery voltage, waiting to “wake up” when the car is started again.
Conclusion: To Unplug or Not to Unplug?
While the parasitic drain from leaving an OBD2 scanner plugged in is usually small, it’s a consistent drain that can impact battery health over time, especially for vehicles used infrequently.
Therefore, it’s generally recommended to unplug your OBD2 scanner when you are not actively using it, especially if you don’t drive your car regularly. This simple practice can help prevent unnecessary battery drain and prolong the life of your car battery. For those who use their cars daily, the impact might be minimal, but for peace of mind and optimal battery health, unplugging is the safer and more proactive approach.
