Disconnecting your car battery can often lead to a frustrating reset of your radio presets, clock, and even more importantly, the learned settings in your car’s control modules that optimize engine performance. While some vehicles allow you to use the accessory power outlet to prevent this memory loss, Subaru WRX models are different. Their outlets are not constantly powered, requiring a different approach. Fortunately, your WRX’s OBD2 port offers a solution.
Understanding the Constant Power Supply: Pin 16 of Your OBD2 Port
The On-Board Diagnostics II (OBD2) port in your Subaru WRX isn’t just for reading trouble codes. Pin 16 of this port is designed to provide constant battery power. This constant power is crucial for modules that need to retain memory even when the ignition is off. This makes it an ideal point to supply temporary power when you need to disconnect your car’s battery for maintenance or replacement.
Alt text: Locating the OBD2 port in a vehicle’s interior, typically under the dashboard on the driver’s side.
Many automotive service centers utilize this feature with specialized adapters. These adapters connect a 12V power source, like a jump starter, through the OBD2 port, effectively bypassing the disconnected car battery and maintaining power to the system. A commonly used fuse for this purpose is a 7.5 Amp fuse, which is generally sufficient for keeping the car’s memory alive.
The 7.5 Amp Fuse: A Critical Safety Measure
The 7.5 Amp fuse is a vital safety component in this process. While the modules requiring constant power draw minimal current, the system isn’t designed to power accessories or high-draw components while running solely through the OBD2 port. If you accidentally turn on the headlights, interior lights, or open a door causing the dome light to activate while the battery is disconnected and power is supplied through the OBD2 port, the increased current draw might exceed the 7.5 Amp limit. This will cause the fuse to blow, effectively disconnecting the temporary power supply, similar to simply disconnecting the battery without any power maintenance.
Alt text: A detailed view of a Subaru WRX engine bay, showcasing the complexity and importance of maintaining electronic settings during battery changes to ensure optimal performance.
Avoiding Memory Loss and Potential Issues
A blown fuse in this scenario isn’t harmful to your WRX, but it defeats the purpose of using the OBD2 port for memory maintenance. You’ll likely notice the clock and radio reset, and the engine’s Electronic Control Module (ECM) might need to relearn its optimal settings, potentially causing a slightly rough idle for a short period after reconnecting the battery.
It’s plausible that if you experience these resets after a battery service, a technician might have attempted to use the OBD2 port method but inadvertently triggered a fuse blow by activating a car accessory during the process.
Importantly, a blown fuse related to this memory-saving technique will not trigger a Check Engine Light (CEL). However, if this fuse is blown, and you attempt to use an OBD2 code reader that relies on the car’s power, it will likely fail to operate, preventing you from reading any stored diagnostic trouble codes.
Conclusion: Smart Battery Disconnection for Your WRX
Using the OBD2 port’s pin 16 to supply temporary power is a clever method to prevent memory loss when disconnecting your Subaru WRX battery. By understanding the limitations of the 7.5 Amp fuse and avoiding unnecessary power draws during the process, you can seamlessly maintain your car’s settings and ensure a smooth restart after battery maintenance. This simple trick can save you time and ensure your WRX continues to run optimally without the need for systems to relearn essential parameters.
