* Security system needs to be reprogrammed: Disconnecting the battery often resets the security system. Your car may need to be reprogrammed to recognize the key fob(s) again. This often requires a visit to a dealership or a locksmith specializing in automotive security.
* Faulty key fob: The battery in your key fob might be dead or the fob itself may be malfunctioning. Try replacing the battery in your key fob(s). If you have multiple fobs, try each one.
* Security module failure: The car's security module itself could be faulty. This is less likely if the problem started *after* the battery change, but it's a possibility if the module was already weakened. A diagnostic scan by a mechanic is needed to confirm this.
* Body control module (BCM) issue: The BCM controls many electrical functions in the car, including the locks and trunk. A problem with the BCM could be causing these issues, potentially exacerbated by the battery disconnect. A diagnostic scan would be necessary to check the BCM.
What you should do:
1. Try replacing the key fob battery: This is the easiest and cheapest thing to try first.
2. Try all your key fobs: If you have multiple keys, make sure they all behave the same.
3. Have the car scanned for diagnostic trouble codes (DTCs): A mechanic or auto parts store with a code reader can scan the car's computer for error codes. This will give you a much clearer indication of the problem.
4. Consider reprogramming the security system: If the scan doesn't reveal a specific failing component, this is the next logical step. A dealer or locksmith is typically needed for this.
Avoid continuing to drive the car with these issues, as the random unlocking and trunk opening pose a security risk.
