When disconnecting a car battery, stored data in various control modules, crucial for vehicle optimization, is lost. Settings like radio presets and the clock are also affected. Some vehicles have always-on accessory power outlets, allowing a 12V supply to maintain power to these systems even with the battery disconnected.
However, Subaru vehicles, including the 2013 Impreza, do not have constantly powered outlets. An alternative power source is needed when disconnecting the battery. The OBDII port, specifically pin 16, provides a continuous connection to the electrical system. This port, often used for diagnostics, can be utilized to maintain power.
Many service centers use adapters to connect a 12V source, like a portable battery, to the OBDII port via a 7.5 Amp fuse. This method works effectively as long as no significant electrical loads are activated within the car. The power draw of the control modules is minimal, well within the fuse’s capacity.
However, actions like opening a door, triggering interior lights, can exceed the 7.5 Amp limit, blowing the fuse. This results in the same data loss as a complete battery disconnection, resetting the clock, radio presets, and potentially causing rough idling until the Engine Control Module (ECM) relearns its parameters.
A blown fuse in the OBDII power supply won’t directly trigger a Check Engine Light (CEL). However, it can prevent code readers that rely on the car’s power from communicating with the OBDII port. A common scenario is a shop attempting to maintain power through the OBDII port during battery replacement, inadvertently overloading the circuit and blowing the fuse. This often manifests as reset clock and radio settings. The 2013 Subaru Impreza’s OBDII port, while useful for maintaining power, requires careful attention to avoid exceeding the fuse capacity.
