Leaving an OBD2 ELM327 plugged into your car’s OBD-II port is a common question among car owners. While convenient, it’s crucial to understand the potential impact on your car’s battery. This article explores the power consumption of OBD2 devices, specifically the ELM327, and whether leaving it connected long-term is advisable.
OBD2 Power Consumption and Your Car’s Battery
OBD-II ports, adhering to international standards like ISO 9141-2 (K-Line), consistently have pin 16 permanently live. This means any device connected to the port receives continuous power, even with the ignition off. While the current draw of an ELM327 is relatively small, typically around 10mA, this constant drain can impact your battery over time. A vehicle’s sleep mode current consumption, usually around 30mA, increases to approximately 40mA with an OBD2 device plugged in. This increase potentially reduces battery life by about 25%.
Frequency of Use and Battery Drain
The impact of leaving an OBD2 ELM327 plugged in depends heavily on how frequently you use your vehicle. For cars driven several times a week, the battery recharges sufficiently, negating the minor drain. However, for vehicles used infrequently, perhaps once a month, the continuous draw can lead to a noticeable battery discharge, requiring charging sooner.
Why Some OBD2 Devices Appear Offline With Ignition Off
Some OBD2 scanners and apps might appear inactive with the ignition off due to two primary reasons. Firstly, certain car manufacturers, like BMW, utilize pin 15 for switched power, a deviation from the standard. This allows BMW-specific diagnostic tools, like INPA, to recognize ignition status. However, this doesn’t apply to generic OBD2 devices.
Secondly, many devices employ battery voltage sensing. When the voltage drops below a threshold, usually around 13.2V, the device assumes the alternator is off and enters a low-power sleep mode. Although seemingly off, it continues monitoring battery voltage, drawing a small current (around 10mA in one tested device), to reactivate when the voltage rises.
Recommendation: Should You Leave it Plugged In?
While the power draw of an ELM327 is minimal, disconnecting it when not in use is generally recommended, especially for infrequent vehicle use. This precaution ensures minimal battery drain and prevents potential long-term battery issues. If you anticipate using your car within a few days, leaving it connected is less of a concern. However, for extended periods of inactivity, disconnecting the device is a prudent practice to preserve battery health.
