For car owners and enthusiasts alike, On-Board Diagnostics (OBD) scan tools have become indispensable for vehicle maintenance and troubleshooting. These devices plug into your car’s OBD port, offering a wealth of data about your vehicle’s health. But a common question arises: can you drive with a scan tool plugged in? Let’s delve into this and understand the implications.
Modern vehicles, especially models like the BMW E46 mentioned in the original context, adhere to OBD standards, often ISO 9141-2 (K-Line). A crucial aspect of these standards is that pin 16 of the OBD port is designed to be permanently powered. This means that anything you plug into this port, including your scan tool, will receive continuous power, even when your car is turned off.
The immediate concern that springs to mind is battery drain. As @All2kool correctly pointed out, a plugged-in scan tool will draw current. While the draw might be minimal, perhaps around 10mA, it’s still a parasitic load on your battery. This additional drain can increase your car’s sleep consumption, potentially shortening the lifespan of your battery, especially if the vehicle is not driven frequently. For daily drivers, this drain might be negligible. However, if your car sits idle for weeks, or even a month, this constant drain could lead to a noticeably weaker battery or even a flat battery when you need your car the most.
You might wonder why some scan tools or apps appear inactive when the ignition is off. There are a couple of reasons for this. Firstly, some manufacturers like BMW have incorporated pin 15 for switched power, which is outside the standard ISO 9141-2. This is often used for manufacturer-specific diagnostics, allowing tools like INPA to detect ignition status. Secondly, and more commonly, many generic scan tools employ voltage sensing to determine if the car is running. They monitor the battery voltage; if it drops below a certain threshold, typically around 13.2v, the tool assumes the engine is off and enters a sleep mode to minimize its own power consumption. Despite appearing off, these devices often remain connected and are still drawing a small amount of current to monitor the battery and ‘wake up’ when the voltage increases, indicating the car is started.
Therefore, while it is technically possible to drive with a scan tool plugged in, and for short trips or regular car use, it might not present an immediate problem, it’s generally advisable to unplug your scan tool when it’s not in active use, especially for prolonged periods of vehicle inactivity. This simple practice helps to prevent unnecessary battery drain and ensures your car battery remains healthy for longer. If you only use your car sporadically, disconnecting the scan tool becomes even more critical to avoid unexpected battery issues. Consider plugging it in only when you need to perform diagnostics and unplugging it after you’re done, as a good practice for vehicle maintenance.
