alarm goes off every time door is opened for a couple minutes

factory or aftermarket??

Roy

Check the driver door switch. It could be faulty and the security system is not recognising that the switch has been unlocked.

By the way if you had used a code reader, you might not see any trouble codes. Only scan tools capable of reading Body Control Module trouble codes would work.

@Roy ---- All factory

@khlow ---- I will try the door switch.

The door switch I meant is the one inside door panel whereby when key is used to unlock, it would send a signal to the BCM to deactivate the security system.

I checked all the connections inside door panel. All seem good. How would I check the door switch if it's faulty or not

Also the car has no brake lights and feels like it has no power brakes.

No brakes lights could be due to a blown fuse underhood and this fuse is also linked to the security system.

You must use a multimeter to test the switch for continuity in order to understand if it is faulty.

Heavy brake pedal effort could mean a bad brake booster or insufficient vacuum boost due to a leaking or clogged hose.