Many car owners use OBD2 scanners for diagnostics, performance monitoring, and accessing real-time vehicle data. A common question arises: can I leave my OBD2 plugged in all the time? To answer this, we need to understand how OBD2 devices draw power and the potential impact on your car’s battery.
OBD2 ports, standardized across modern vehicles, are designed to provide constant power. Pin 16 of the OBD2 port is always live, as mandated by international standards. This means that anything plugged into your OBD2 port, including scanners and adapters, will continuously draw power, even when your car is turned off.
While the power draw of most OBD2 devices is minimal, it’s not zero. @All2kool correctly points out that even a small current draw can contribute to parasitic battery drain. A typical OBD2 scanner might draw around 10mA in sleep mode. In isolation, this seems insignificant. However, when added to the car’s inherent sleep consumption (around 30mA for many vehicles), it can increase the total drain to 40mA.
What does this mean for your car battery? This additional drain can shorten the lifespan of your battery, especially if you don’t drive your car frequently. If your car is used daily or every few days, the alternator will easily compensate for this minor drain during normal operation. You likely won’t notice any difference. However, if your car sits for extended periods – weeks or months – the cumulative effect of even a small parasitic draw can become significant, potentially leading to a dead battery.
Some users might observe that their OBD2 apps or readers don’t seem to be active when the ignition is off. This can be due to a couple of reasons. Firstly, some car manufacturers, like BMW, have used pin 15 for switched power in addition to the standard pin 16. This is often used for manufacturer-specific diagnostic tools to detect ignition status. Secondly, and more commonly, many generic OBD2 devices and apps employ voltage sensing to determine the car’s on/off state. They monitor the battery voltage; if it drops below a certain threshold, typically around 13.2V, they assume the engine is off and enter a sleep mode to minimize their own power consumption. Even in sleep mode, these devices often still draw a small current to monitor voltage and “wake up” when the car is started again.
In conclusion, while leaving an OBD2 scanner plugged in continuously might seem convenient, it does introduce a parasitic battery drain. For daily drivers, the impact is negligible. However, if you infrequently use your vehicle or store it for longer periods, it’s advisable to unplug your OBD2 device to prevent unnecessary battery drain and ensure your car starts reliably when you need it. For peace of mind, especially if you’re not using the features of your OBD2 device constantly, disconnecting it when the car is not in use is a simple step to maintain optimal battery health.
