Disconnecting your car battery is a common procedure for maintenance or replacement, but it can lead to the loss of important settings and data stored in your vehicle’s control modules. Many modern vehicles rely on constant power to retain “learned” data that optimizes engine performance, along with convenience features like radio presets and clock settings. When this power is interrupted, these settings are lost, potentially leading to temporary inconveniences or even impacting how your car runs initially.
In some vehicles, you can use the accessory power outlet to maintain power while changing the battery. By connecting a 12V power source to the outlet, you can keep the electrical system energized, preventing memory loss. However, Subaru vehicles, including the 2002 Subaru Outback, often don’t have constantly powered accessory outlets. This means you need to find an alternative power source to prevent your radio presets from vanishing and your engine control module (ECM) from needing to relearn its parameters.
Fortunately, your 2002 Subaru Outback, like many other vehicles, offers a solution through its On-Board Diagnostics II (OBD2) port. Pin 16 of the OBD2 port is designed to be always powered, making it a convenient point to connect a temporary power supply during battery disconnection.
Many automotive service professionals utilize adapters that connect a 12V power source, such as a jump starter or battery maintainer, to the OBD2 port. This connection, often protected by a 7.5 Amp fuse, effectively supplies power to the car’s essential electronic systems, allowing you to disconnect the battery without erasing crucial memory.
Alt text: Locating the OBD2 port underneath the dashboard of a car interior, a common location for diagnostic access.
It’s crucial to remember a key precaution when using this method: ensure that all vehicle accessories are turned off. The power draw from modules and memory retention is minimal and well within the 7.5 Amp fuse rating. However, if you inadvertently open a door, activating interior lights, or switch on other accessories, the increased current draw could exceed the fuse’s capacity. If the current demand surpasses 7.5 Amps while the car battery is disconnected, the fuse will blow – as it is designed to do to protect the system. The result of a blown fuse in this scenario is the same as if you hadn’t used a memory saver at all: loss of presets and settings.
This situation – accidentally blowing the memory saver fuse – is quite common. The telltale signs are a reset clock and radio, and potentially a slightly rougher idle immediately after reconnecting the battery as the ECM begins the “relearning” process.
It’s conceivable that if you recently had your battery replaced and noticed these symptoms, the technician might have attempted to use the OBD2 port for memory saving but inadvertently triggered something in the car, causing the fuse to blow.
It’s important to clarify that this fuse, related to maintaining constant power through the OBD2 port for memory saving, is unrelated to check engine lights (CELs). Blowing this fuse will not cause a CEL to illuminate. However, a blown fuse will prevent a code reader that relies on the car’s power from functioning when plugged into the OBD2 port. This is because pin 16, which provides power to many code readers, will be unpowered if the fuse is blown.
In summary, utilizing the OBD2 port, specifically pin 16, on your 2002 Subaru Outback is a viable method for maintaining your car’s memory when disconnecting the battery. By using a memory saver device connected to the OBD2 port and ensuring all accessories are off, you can avoid the inconvenience of lost settings and ensure a smoother engine operation after a battery change. Just be mindful of the 7.5 Amp fuse and avoid drawing excessive power during the process.
Alt text: Detailed view of an OBD2 port connector, emphasizing pin assignments and highlighting pin 16 as the power source.
