Disconnecting your car battery can lead to more than just a reset clock. In your 2002 Subaru WRX, like many modern vehicles, the Engine Control Module (ECM) and other systems store learned data vital for optimal performance. Losing power means losing this data, along with your radio presets and other settings. Fortunately, the OBD2 port can be a lifesaver.
While some cars allow you to use the accessory power outlet to maintain power during a battery change, Subaru, including the 2002 WRX, doesn’t work this way. Their accessory outlets aren’t constantly powered. So, where can you tap into a constant power source? The answer lies in your 2002 WRX’s OBD2 port, specifically pin 16. This pin is designed to be always hot, providing constant power to the system.
Many auto shops utilize this feature with specialized adapters. These adapters connect a 12V power source, like a jump starter, through the OBD2 port, using the port’s built-in 7.5 Amp fuse for protection. This method effectively keeps your 2002 WRX’s systems powered while you swap the battery, preventing memory loss.
Alt text: Location of the OBD2 port in the interior of a 2002 Subaru WRX, typically found under the dashboard on the driver’s side.
However, it’s crucial to remember the 7.5 Amp fuse limitation. The modules themselves draw minimal power, so maintaining memory isn’t a problem. The risk arises if anything in the car is switched on during the battery replacement. For example, simply opening a door can activate interior lights, potentially drawing several amps. If the total current draw exceeds 7.5 Amps while the car battery is disconnected and powered through the OBD2 port, the fuse will blow – as it’s designed to do. The result is the same as if you hadn’t used the OBD2 port trick at all: lost presets and potentially a rough idle until the ECM relearns.
Alt text: A close-up of a blown 7.5 amp fuse, highlighting the melted filament inside, indicating an electrical overload when using the OBD2 port for power during a battery change in a 2002 WRX.
A blown fuse in this scenario won’t trigger a Check Engine Light (CEL). However, it will prevent an OBD2 code reader from powering up and reading codes if the reader relies on the car’s power. So, if you find your radio and clock reset after a battery change, and perhaps experience a temporary rough idle with your 2002 WRX, it’s possible a shop attempted to use the OBD2 port for power maintenance but inadvertently blew the fuse. Always ensure all accessories are off when using this method to avoid fuse issues and keep your 2002 WRX’s settings intact.
