When you disconnect your car battery, you might notice that your radio presets are gone, the clock is reset, and even your engine’s performance feels a bit off for a while. This is because modern cars, including the 2015 Subaru WRX, rely on constant power to retain settings and learned data within their control modules. Fortunately, there’s a way to prevent this memory loss when you need to disconnect your battery, and it involves the OBD2 port.
Why Battery Disconnection Resets Your Car’s Systems
Modern vehicles are equipped with numerous electronic control modules that manage everything from engine performance to infotainment settings. These modules learn and store data to optimize your car’s operation. For example, the engine control module (ECM) learns your driving habits to fine-tune fuel delivery and ignition timing. Disconnecting the battery interrupts the power supply to these modules, causing them to lose this “learned” information, along with convenient settings like your radio stations and clock.
The OBD2 Port Solution for Your 2015 WRX
While some vehicles allow you to maintain power through the accessory power outlet during a battery change, this method doesn’t work on all cars, including Subarus like the 2015 WRX. This is because the accessory outlets in many Subarus are not constantly powered. However, your 2015 WRX, like most modern cars, has an OBD2 (On-Board Diagnostics II) port, and crucially, pin 16 of this port is always connected directly to the car’s electrical system and battery. This constant power supply makes the OBD2 port a viable point to introduce external power and keep your car’s memory intact during a battery change.
How to Use the OBD2 Port to Maintain Power
Automotive service centers often use a specialized adapter that connects a 12V power source, such as a jump starter or battery maintainer, to the OBD2 port. This adapter typically incorporates a 7.5 Amp fuse for safety. By connecting your 12V source to the OBD2 port using such an adapter, you can supply power to the car’s essential systems while the main battery is disconnected. This prevents memory loss and keeps your settings and learned data preserved.
Important Precautions: Fuse Safety
The 7.5 Amp fuse in these OBD2 port adapters is a crucial safety feature. It’s designed to protect the car’s electrical system from overload. While the modules requiring constant power draw very little current, activating other electrical components in the car can easily exceed the 7.5 Amp limit. For instance, simply opening a door and turning on the interior lights could draw more than 7.5 Amps. Therefore, it’s essential to ensure that absolutely nothing in the car is turned on when using this method. If the current draw exceeds 7.5 Amps while the car battery is disconnected, the fuse will blow, effectively cutting off the power supply and resulting in memory loss, just as if you had disconnected the battery without any power maintenance.
What Happens if the Fuse Blows?
If the 7.5 Amp fuse blows during this process, the immediate consequence is the same as if you had simply disconnected the battery without maintaining power. Your radio presets and clock will reset, and the engine control module might exhibit a rough idle for a short period as it “relearns” optimal settings. This is often a common and unintentional occurrence, easily identified by the reset clock and radio.
OBD2 Port and Diagnostic Tools
It’s important to note that a blown fuse in this scenario, specifically the one used for maintaining memory via the OBD2 port, will not trigger a Check Engine Light (CEL). However, if you attempt to use an OBD2 code reader that relies on the car’s power to operate after blowing this fuse, it may fail to power up and read any diagnostic codes. This is because the blown fuse interrupts the power supply to the OBD2 port itself.
Conclusion
Using the OBD2 port to maintain power during a battery change on your 2015 WRX is a viable technique to prevent memory loss. However, it’s crucial to proceed with caution and ensure no electrical accessories are activated to avoid blowing the 7.5 Amp fuse. By understanding the function of the OBD2 port and taking necessary precautions, you can seamlessly replace your 2015 WRX battery without losing your preferred settings and engine learning data.
