The OBD2 port on a 2015 Subaru WRX, like in most vehicles, plays a crucial role in diagnostics. However, it can also be utilized to maintain power to the car’s computer systems during a battery replacement, preventing the loss of learned data and settings. This article will discuss why this is necessary and how it can be done safely.
Why Maintain Power During Battery Disconnection?
Modern cars rely on various control modules that constantly learn and adapt to optimize performance. When the battery is disconnected, these modules lose power and, consequently, this learned data. This can lead to issues like rough idling, reset radio presets, and a lost clock setting. Unlike some vehicles, Subaru accessory power outlets are not constantly powered, making them unsuitable for maintaining power during battery disconnection.
Utilizing the OBD2 Port for Power
The OBD2 port offers a solution. Pin 16 of the OBD2 connector provides a constant 12V power source. Using a special adapter, a technician can connect a 12V power source, such as a portable battery, to this pin, maintaining power to the essential systems. This process typically involves a 7.5 Amp fuse in the adapter for protection.
Precautions When Using the OBD2 Port
While using the OBD2 port for power, it’s critical to ensure nothing in the car is turned on. The minimal power draw of the modules is well within the 7.5 Amp fuse limit. However, activating interior lights, for example, can significantly increase the current draw, potentially exceeding the fuse’s capacity and causing it to blow. This would interrupt the power supply, resulting in the same data loss as a complete battery disconnection.
Common Issues and Misconceptions
A blown fuse in the OBD2 power adapter is a common occurrence, often resulting in reset clocks and radios. It’s crucial to understand that this blown fuse itself doesn’t trigger a Check Engine Light (CEL). However, it can prevent a code reader from communicating with the car’s computer if the reader relies on the vehicle’s power. If you experience data loss after a battery replacement, a blown fuse in the OBD2 adapter might be the culprit. The technician may have inadvertently activated a component in the car, overloading the circuit. Always consult a qualified technician if you encounter issues.
