As a Subaru Impreza owner, you might have encountered the minor inconvenience of losing your radio presets and clock settings after a battery disconnect. This is a common occurrence across many vehicles, stemming from the loss of power to various control modules that store learned data essential for optimal vehicle performance. While this reset might seem trivial, it can also affect engine performance as the car’s computer relearns settings. Fortunately, there’s a way to prevent this memory loss in your Subaru Impreza, and it involves a familiar port: the OBD2 port.
In many vehicles, maintaining power during a battery change is straightforward. Often, the accessory power outlet remains live even when the ignition is off, allowing a 12V power source to be connected, thus preserving the vehicle’s electronic memory. However, Subaru vehicles, including the Impreza, typically don’t offer this convenience. Their accessory outlets are not constantly powered, requiring an alternative solution to keep the system energized during battery swaps or disconnections.
The solution lies within your Impreza’s On-Board Diagnostics II (OBD2) port. Pin 16 of this port is designed to be always hot, meaning it’s constantly connected to the vehicle’s electrical system, even when the car is off. This constant power supply makes it an ideal point to introduce temporary power and prevent memory loss during battery disconnection.
Many automotive service professionals utilize specialized adapters that connect a 12V power source, such as a jump starter or battery maintainer, directly through the OBD2 port. This connection, often fused at 7.5 Amps, provides just enough power to keep the sensitive electronic modules alive while the main battery is disconnected. It’s a simple yet effective workaround for Subaru vehicles like the Impreza.
However, it’s crucial to exercise caution when using this method. The 7.5 Amp fuse is designed for the minimal power draw of the control modules and memory functions. Activating any significant electrical components within the car, such as interior lights by opening a door, can overload this circuit. If the current draw exceeds 7.5 Amps, the fuse will blow, effectively negating the purpose of the power supply and resulting in the same memory loss you were trying to avoid. This is analogous to simply disconnecting the battery without any power maintenance – your presets will be lost, and the engine control module (ECM) might need to relearn its parameters, potentially causing a temporary rough idle.
It’s quite possible that a blown fuse is the culprit if you’ve attempted to maintain power through the OBD2 port and still experienced a reset. While this blown fuse won’t trigger a Check Engine Light (CEL) directly, it can prevent an OBD2 code reader from functioning correctly if the reader relies on the car’s power from the port.
Therefore, when disconnecting your Subaru Impreza’s battery, utilizing the OBD2 port with a 12V power maintainer is a viable method to preserve your settings and prevent ECM relearning. Just remember to ensure all accessories are off and avoid opening doors or activating any power-drawing components while the main battery is disconnected and power is supplied solely through the OBD2 port. This simple step can save you the minor frustration of resetting your car’s memory and ensure a smoother driving experience immediately after a battery change.
