For Subaru WRX owners, a simple task like changing your car battery can sometimes lead to unexpected frustrations. Disconnecting the battery in most vehicles, including your WRX, results in a loss of power to various electronic control modules. This means you could lose important “learned” data that optimizes your car’s performance, along with the annoyance of reset radio presets and clock.
While some cars allow you to use the accessory power outlet to maintain power during a battery change, Subaru vehicles, including the WRX, are different. Their outlets are not constantly powered, rendering this common method ineffective. So, how do you avoid losing your settings when replacing your Subaru WRX battery? The answer lies in your OBD2 port.
The Subaru Challenge: Why Battery Disconnect Resets Settings
Modern cars like the Subaru WRX rely heavily on computers to manage various functions, from engine performance to entertainment systems. These control modules store learned information and personalized settings. When battery power is completely cut off, these modules can lose volatile memory. This results in:
- Reset Radio Presets and Clock: Your saved radio stations and clock settings will revert to default.
- Potential Engine Performance Issues: The engine control module (ECM) might need to relearn optimal settings, potentially causing rough idling or slightly reduced performance for a short period after reconnecting the battery.
This can be a minor inconvenience, but for WRX enthusiasts who value optimized performance and personalized settings, it’s something to avoid.
Utilizing Your WRX OBD2 Port for Power: A Smart Solution
Fortunately, there’s a clever workaround for Subaru vehicles like the WRX. The On-Board Diagnostics II (OBD2) connector, typically used for reading diagnostic codes, has a pin that is constantly powered – pin 16. This constant power supply makes the OBD2 port a potential point to introduce temporary power while the battery is disconnected.
Many professional service centers are aware of this trick and utilize specialized adapters. These adapters connect a 12V power source, like a portable jump starter, to the OBD2 port, specifically through pin 16. This provides just enough power to the car’s essential systems to retain memory settings while the main battery is disconnected for replacement.
Important Considerations: The 7.5 Amp Fuse and Avoiding Issues
This OBD2 power method is effective, but it’s crucial to understand the limitations and potential pitfalls. The circuit powering the OBD2 port is usually protected by a 7.5 Amp fuse. This fuse is designed to protect the system from overload.
Here’s what you need to be aware of:
- Fuse Protection: The 7.5 Amp fuse is sufficient for maintaining the memory of the control modules, which draw minimal power.
- Overload Risk: If you accidentally turn on any significant electrical accessory in the car while the battery is disconnected and power is supplied through the OBD2 port, you risk blowing this 7.5 Amp fuse. Even opening a door and activating interior lights could potentially draw enough current to exceed 7.5 Amps and blow the fuse.
Consequences of a Blown Fuse: If the 7.5 Amp fuse blows during this process, the result is the same as if you hadn’t used the OBD2 method at all – you will lose your settings. Importantly, a blown fuse in this circuit will not trigger a Check Engine Light (CEL). However, it will prevent an OBD2 code reader that relies on the car’s power from functioning until the fuse is replaced.
Best Practices for Maintaining Power via OBD2 on your WRX
To successfully use the OBD2 port to maintain your Subaru WRX settings during a battery change and avoid blowing the fuse, follow these precautions:
- Ensure All Accessories are OFF: Before disconnecting the battery and connecting the external 12V power source to the OBD2 port, make absolutely sure that everything in your car is turned off. This includes headlights, interior lights, radio, climate control, and any aftermarket accessories.
- Avoid Opening Doors: As mentioned, even interior lights can draw enough current to blow the fuse. Try to keep doors closed during the battery replacement process, or at least be mindful of minimizing interior light usage.
- Use a Proper Memory Saver Tool: For DIYers, consider purchasing a dedicated OBD2 memory saver tool. These tools often come with built-in fuse protection and are designed specifically for this purpose, making the process safer and more convenient.
By understanding the OBD2 power method and taking necessary precautions, you can ensure a smooth battery replacement on your Subaru WRX without losing your important settings and configurations. This simple trick can save you time and frustration, keeping your WRX running optimally and personalized just the way you like it.
