* Faulty Body Control Module (BCM): This is a computer that controls many electrical functions, including the lights. A malfunctioning BCM is a likely suspect if other electrical issues are present.
* Wiring Problem: A short circuit or damaged wire in the lighting circuit could be keeping power flowing to the lights even when the ignition is off. This could be anywhere from the switch to the lights themselves.
* Faulty Light Switch: The switch itself might be failing, allowing power to remain on even when in the "off" position.
* Faulty Relay: Relays act as switches for various circuits. A faulty relay controlling the running lights could be stuck in the "on" position.
* Aftermarket Accessories: Recently installed aftermarket accessories or modifications (especially those involving the electrical system) might have introduced a fault.
* Battery Drain: While this isn't the *cause* of the lights staying on, a constantly draining battery could be *related*. The lights are constantly drawing power, leading to a dead battery. You need to address the root cause (the lights staying on) first.
Troubleshooting Steps:
1. Check the fuses: Start by checking the fuses related to the running lights in the fuse box (usually under the hood and/or in the cabin). A blown fuse might indicate a short circuit somewhere. However, if the fuse is good, it suggests the problem is further back in the circuit.
2. Test the light switch: If you can safely access the switch (likely requiring some disassembly), try testing its continuity to see if it's breaking the circuit properly when in the "off" position. This requires basic electrical testing knowledge and tools.
3. Inspect the wiring: Visually inspect the wiring harness leading to the running lights. Look for any signs of damage, fraying, or corrosion.
4. Check the BCM: A professional diagnostic scan using an OBD-II reader that can communicate with the BCM is likely required to determine if the BCM is faulty. A mechanic can read the trouble codes and diagnose.
5. Disconnect the battery: This will stop the drain, but won't fix the underlying problem. It's a temporary solution to prevent battery damage.
Recommendation:
Unless you have experience working with automotive electrical systems, it's best to take your Impreza to a qualified mechanic or an auto electrician. They have the tools and expertise to diagnose the problem accurately and perform the necessary repairs safely. Attempting to fix this without proper knowledge could damage your car's electrical system further.
