Maintaining your 1999 Subaru Legacy Outback in peak condition requires understanding its diagnostic systems. A key component for both professional mechanics and DIY enthusiasts is the On-Board Diagnostics II (OBD2) port. This port is not only crucial for reading trouble codes but also serves a handy purpose when you need to disconnect your car battery without losing important settings. Let’s dive into the specifics of the OBD2 port location on your 1999 Subaru Legacy Outback and how it can be utilized.
Finding the OBD2 Port in Your 1999 Subaru Legacy Outback
Locating the OBD2 port is usually straightforward. For the 1999 Subaru Legacy Outback, you’ll typically find it located inside the cabin on the driver’s side. Specifically, you should look under the dashboard, in the area above your knees. It’s often near the steering column or slightly to the left. The port is a trapezoid-shaped, 16-pin connector, and it’s designed to be easily accessible for diagnostic tools.
[Imagine an image of a person pointing to the OBD2 port under the dashboard of a car, similar to where it would be in a 1999 Subaru Legacy Outback. If there was an image in the original article, I would use it here with proper alt text.]
Why the OBD2 Port Matters for Your Subaru
The OBD2 port is your gateway to your car’s computer. It allows mechanics and car owners to:
- Read Diagnostic Trouble Codes (DTCs): When your check engine light illuminates, the OBD2 port is used to connect a scan tool or code reader. This tool retrieves DTCs, which are codes that pinpoint potential problems within your vehicle’s systems.
- Clear Trouble Codes: After repairs are made, the OBD2 port can be used to clear the stored trouble codes and turn off the check engine light.
- Access Real-Time Data: Advanced scan tools can display live data from your engine and other systems, helping diagnose intermittent issues or monitor performance.
- Maintain Power During Battery Disconnection: As we’ll discuss further, the OBD2 port can be used to supply temporary power to your car’s computer when disconnecting the battery.
Using the OBD2 Port to Maintain Power During Battery Changes
Disconnecting your car battery can lead to the loss of “learned” data in your car’s control modules. This can affect engine performance until the car “relearns” these settings. Additionally, you’ll lose radio presets and clock settings.
While some vehicles allow you to use the accessory power outlet to maintain power during battery changes, this method does not work on Subarus, including the 1999 Legacy Outback. Subaru accessory outlets are not constantly powered.
However, the OBD2 port offers an alternative. Pin 16 of the OBD2 connector is constantly powered, making it a viable point to connect a 12V power source to maintain your car’s memory while the battery is disconnected.
Many automotive service centers utilize adapters that connect a 12V source, like a jump starter or battery maintainer, to the OBD2 port via pin 16. This is often done with a 7.5 Amp fused adapter for safety.
Important Considerations and Potential Issues
While using the OBD2 port for power maintenance is helpful, it’s crucial to be aware of potential issues:
- Fuse Limit: The circuit powering the OBD2 port is typically protected by a 7.5 Amp fuse. This is sufficient for keeping the control modules powered and retaining memory. However, do not turn on any accessories like interior lights, headlights, or the radio while the battery is disconnected and power is supplied through the OBD2 port. Activating these could draw more than 7.5 Amps and blow the fuse.
- Blown Fuse Consequences: If the fuse blows, you will lose power to the modules, defeating the purpose of using the OBD2 port for memory retention. You’ll experience the same issues as if you had simply disconnected the battery – loss of radio presets, clock reset, and potentially rough idling until the engine control module (ECM) relearns.
- No Check Engine Light (CEL) from Blown Fuse: A blown fuse in this circuit will not trigger a check engine light. However, if you try to use an OBD2 code reader that relies on the car’s power, it may not function because of the blown fuse.
Best Practices for Using the OBD2 Port for Battery Swaps
To safely and effectively use the OBD2 port to maintain power during a battery replacement on your 1999 Subaru Legacy Outback:
- Locate the OBD2 port as described earlier.
- Use a Memory Saver: Purchase a dedicated OBD2 memory saver tool. These are readily available and designed for this specific purpose. They typically include a cable with an OBD2 connector, a 12V power plug (for another car’s accessory outlet or a jump starter), and a fuse.
- Connect the Memory Saver: With the ignition OFF and all accessories off, connect the OBD2 memory saver to your car’s OBD2 port.
- Connect to Power Source: Connect the other end of the memory saver to a 12V power source (another car’s battery or a jump starter). Ensure the power source is stable and providing a consistent 12V supply.
- Disconnect the Battery: Now you can safely disconnect your 1999 Subaru Legacy Outback’s battery for replacement or maintenance.
- Replace Battery and Reconnect: Install the new battery and reconnect the terminals.
- Disconnect Memory Saver: After the new battery is securely installed, disconnect the memory saver tool from the OBD2 port and the external power source.
By understanding the OBD2 port location and its power capabilities in your 1999 Subaru Legacy Outback, you can confidently perform battery replacements and diagnostic procedures while minimizing data loss and ensuring a smoother car maintenance experience.
